Diagnosis - 4l60-e Chevrolet Caprice Impala SS

APPLICATION

4L60-E APPLICATION

DESCRIPTION

The 4L60-E transmission uses 2 electric shift solenoids to control transmission upshifts and downshifts. In addition, a pressure control (force motor) solenoid controls hydraulic line pressure, and a Torque Converter Clutch (TCC) solenoid controls TCC application. A TCC Pulse Width Modulated (PWM) solenoid is used to control fluid acting on converter clutch valve, which then controls TCC apply and release. A 3-2 control solenoid modulates hydraulic pressure for the 2-4 band and 3-4 clutch to improve 3-2 downshift. Solenoids are turned on and off by Powertrain Control Module (PCM).

PCM receives signals from various transmission sensors. Sensors include engine speed and throttle position, transmission speed, hydraulic pressure and transmission fluid temperature. PCM has on-board self-diagnostics to help identify any parts or circuits which may need further testing.

OPERATION

Shift solenoid holds hydraulic pressure (solenoid on) or releases hydraulic pressure (solenoid off). This action controls shift valves inside valve body. By switching one or both solenoids on or off, different combinations of clutches, sprags and bands are operated. See CLUTCH & BAND APPLICATION under TROUBLE SHOOTING.

PCM

PCM is located under air cleaner on Caprice, Fleetwood, Impala SS and Roadmaster, at right rear corner of engine compartment on Camaro and Firebird, and above power brake booster on Corvette.

On light trucks and vans (gasoline), PCM is located behind glove box on "C" and "K" series vehicles, under driver's seat on "G" series vehicles, or at right rear corner of engine compartment on "L", "M", "S" and "T" series vehicles. For series identification, see BODY CODE in APPLICATION table.

On light trucks and vans (diesel), PCM is located behind right side of dash on "C" and "K" series truck. PCM is located under driver's seat or behind right side of dash on "G" series van. PCM controls TCC, pressure control solenoid, (hydraulic pressure), PWM solenoid and shift solenoids 1-2 and 2-3. In addition, PCM also controls ignition, fuel and emission devices related to engine.

PCM receives electronic signals from sensors and switches. These signals help PCM determine when to operate various relays and solenoids related to engine and transmission components.

SENSORS & SWITCHES

PCM controls converter clutch lock-up, upshifts and downshifts based on transmission temperature, system voltage, throttle position, transmission oil pressure switches (5), and transmission output and input (engine) speed sensors. (Scheme 39) System includes several other sensors and switches that are used for engine control (gasoline engines). For additional information and testing of engine components, see appropriate SYSTEM/COMPONENT TESTS article in ENGINE PERFORMANCE section.

Shift Solenoids 1-2 & 2-3

Transmission is shifted up or down by 2 electric shift solenoids. Both solenoids are located on valve body. (Scheme 39) Ignition power is supplied to each solenoid by transmission fuse. Solenoid 1-2 controls hydraulic pressure to 1-2 shift valve. Solenoid 2-3 controls hydraulic pressure to 2-3 shift valve.

Note. The 3-4 shift valve is directly controlled by hydraulic circuits in valve body.

Pressure Control

Pressure control (force motor) solenoid has a spool valve and operates pressure regulator valve. (Scheme 39) PCM sends a frequency signal to pressure control solenoid to regulate hydraulic line pressure. Frequency signal (duty cycle) is measured with a dwell meter or lab scope. When duty cycle is zero, line pressure is at maximum, and pressure control solenoid draws zero amps. When duty cycle is 60 percent, line pressure is at minimum, and pressure control solenoid draws 1.1 amps at 4.5 volts.

Locating Transmission Solenoids, Sensors & Switches Courtesy of General Motors Corp. Scheme 39

TCC Solenoid

This solenoid is used to control TCC apply valve. PCM sends a frequency signal to TCC solenoid to gradually apply or release TCC. (Scheme 39)

3-2 Control Solenoid

PCM modulates current (duty cycle) to control 3-2 control solenoid. The 3-2 control solenoid is off in first gear. In all other gears, 3-2 control solenoid is 90 percent on. Hydraulic pressure is regulated to smoothly release 3-4 clutch and 2-4 band during 3-2 downshift.

TCC PWM Solenoid

TCC PWM solenoid is used to control fluid acting on converter clutch valve, which then controls TCC apply and release. (Scheme 39) TCC PWM solenoid is used to provide smooth engagement of torque converter clutch by operating on a negative duty cycle percent of on time.

SELF-DIAGNOSTICS

PCM constantly monitors all electrical circuits. If PCM detects circuit problems or sensors out of range, it will record a Diagnostic Trouble Code (DTC). If problem continues for a predetermined time, Malfunction Indicator Light (MIL) will glow.

If MIL is on all the time, DTC(s) are currently being detected. If MIL is off, but PCM had detected a circuit or sensor problem, DTC(s) will be stored in computer memory.

Stored DTCs may be retrieved from PCM memory. Depending on vehicle, several methods may be used. The most basic method (non-scan) uses a jumper wire to activate MIL, which will flash a series of codes. Other method includes using a factory recommended Tech 1 scan tool or aftermarket scan tool.

Note. Faulty engine sensors and actuators may cause transmission related DTCs or driveability problems. Engine faults and related DTCs must be diagnosed and repaired before transmission codes are repaired. For additional information on diagnosing and repairing engine-related PCM trouble codes, see appropriate TESTS W/CODES article in ENGINE PERFORMANCE section.

TROUBLE SHOOTING

Note. For trouble shooting procedures, see TROUBLE SHOOTING in the AUTO TRANS OVERHAUL - 4L60-E article.

CLUTCH & BAND APPLICATION

CLUTCH & BAND APPLICATION CHART (4L60-E)

ELECTRONIC SELF-DIAGNOSTICS

Note. To test electronic control of transmission solenoids without using self-diagnostics or if self-diagnostics does not function, go to COMPONENT TESTS under ELECTRONIC TESTING. After repairs are made, trouble codes should be erased from computer memory. See CLEARING TROUBLE CODES under ELECTRONIC SELF-DIAGNOSTICS.

RETRIEVING CODES WITHOUT SCAN TOOL - GASOLINE ENGINES

Note. Following procedure is for vehicles equipped with a 12-pin Data Link Connector (DLC). On vehicles equipped with 16-pin DLC (OBD-II vehicles), DTCs can only be retrieved using scan tool.

Scheme 40

1. Turn ignition on. DO NOT start engine. MIL should glow. Locate Data Link Connector (DLC) attached to control module wiring harness. Most DLCs are located under dash on driver's side of vehicle. Turn ignition on with engine not running. Connect jumper wire from terminal "B" (diagnostic test terminal) to terminal "A" (ground) of DLC. (Scheme 40) NOTE: Connecting jumper wire into test and ground terminals of DLC with engine running will cause fuel injected vehicles to enter field service mode. MIL will not indicate codes if this is done. (Scheme 40): DLC Terminal Identification Courtesy of General Motors Corp.
2. MIL should begin to flash codes. Each code will be repeated 3 times. For example, FLASH, FLASH, pause, FLASH, longer pause, identifies Code 21. First series of flashes is first digit of trouble code. Second series of flashes is second digit of trouble code.
3. Trouble codes are displayed starting with lowest numbered code. Codes will continue to repeat as long as DLC test terminal is grounded. If codes are not flashed, or MIL does not glow, self-diagnostics will not work. For diagnosis of this condition, see DIAGNOSTIC CIRCUIT CHECK in appropriate BASIC TESTING article in ENGINE PERFORMANCE section. To exit diagnostic mode, turn ignition off and remove jumper wire from DLC.

Note. Trouble codes will be recorded at various operating times. Some codes require operation of affected sensor or switch for 5 seconds; others may require operation for 5 minutes or longer at normal operating temperature, road speed and load. Therefore, some codes may not set in a service bay operational mode and may require road testing vehicle in order to duplicate condition under which code will set.

RETRIEVING CODES WITH SCAN TOOL - GASOLINE ENGINES

Note. Plugging scan tool into DLC enables user to read trouble codes and check voltages in system on serial data line.

Scan tools may also furnish information on status of output devices (solenoids and relays). However, status parameters are only an indication that output signals have been sent to devices by control module; they do not indicate if devices have responded properly to signal. Check for proper response at output device using a voltmeter or test light.

If trouble codes are not present, this is not necessarily an indication a problem does not exist. Driveability related problems with codes displayed occur about 20 percent of the time, while driveability problems without codes occur about 80 percent of the time. Sensors that are out of specification WILL NOT set a trouble code but WILL cause driveability problems. Using scan tool is the easiest method of checking sensor specifications and other data parameters. Scan tool is also useful in finding intermittent wiring problems by wiggling wiring harness and connections (key on, engine off) while observing scan tool.

Note. If erroneous voltage signals are suspected, it will be necessary to verify scan tool information using a digital voltmeter and wiring schematic. If non-existent codes are displayed, turn ignition off, remove scan tool, turn ignition on and ground DLC test terminal "B". (Scheme 40) Same codes flashed by MIL should be indicated by scan tool.

Preliminary Inspection

1. Check all vacuum hoses for correct routing, restrictions, cuts or other damage. Inspect difficult-to-see vacuum hoses beneath air cleaner assembly and other engine components.
2. Inspect all engine compartment wiring for proper connections. Also check wires for pinched or chafed spots, as well as contact with sharp edges or exhaust manifolds.
3. The preliminary inspection is very important and should be performed carefully and thoroughly, as it can often fix a problem without requiring further diagnosis.

Note. Begin all diagnosis with ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK chart. After any DEC/electronically-controlled transmission systems repair, repeat On-Board Diagnostic (OBD) system check.

Diagnostic Procedure

1. Ensure all non-controlled systems NOT related to the Diesel Electronic Control (DEC)/electronically-controlled transmission systems are operating properly. DO NOT proceed with testing unless all non-DEC/electronically-controlled transmission systems problems are repaired.
2. ALWAYS begin diagnosis with On-Board Diagnostic (OBD) system check to determine if DEC/electronically-controlled transmission systems and PCM are working properly. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK chart. Refer to LIGHT TRUCKS & VANS (DIESEL) diagnostic charts. If trouble codes, other than Diagnostic Trouble Code (DTC) 12 are displayed, determine if they are hard or intermittent trouble codes.
3. A hard code is present while working on vehicle, and problem persists. Hard codes will cause Malfunction Indicator Light (MIL) to come on. NOTE: SERVICE ENGINE SOON light, located on instrument cluster, is also referred to as the Malfunction Indicator Light (MIL).
4. An intermittent code does not reset itself and is NOT present while working on vehicle. Intermittent codes are often caused by loose connections. MIL will go out 10 seconds after fault goes away.

Entering Or Exiting Diagnostic Mode

1. With ignition on and engine off, connect a jumper wire between Data Link Connector (DLC) terminal "B" (diagnostic terminal) and terminal "A" (ground). (Scheme 40) Diesel Electronic Control (DEC)/electronically-controlled transmission systems will enter diagnostic mode.
2. In this mode, PCM will display DTC 12 by flashing the MIL once, followed by a short pause, then 2 flashes in quick succession. DTC 12 will be displayed 3 times. If no other codes are stored, DTC 12 will continue to flash until diagnostic terminal is ungrounded. To exit diagnostic mode, turn ignition off and remove jumper from DLC.

TROUBLE CODE DEFINITIONS

Note. Only transmission-related trouble codes are listed. For engine-related DTCs, see appropriate TESTS W/CODES article in ENGINE PERFORMANCE section. Engine-related DTCs must be repaired first, as engine performance and related component signals will affect transmission operation and diagnosis.

PCM TROUBLE CODE DEFINITIONS (CARS)

PCM TROUBLE CODE DEFINITIONS (LIGHT TRUCKS & VANS - GASOLINE EXCEPT "S" & "T" 4.3L VIN W)

PCM TROUBLE CODE DEFINITIONS (LIGHT TRUCKS & VANS - DIESEL)

PCM TROUBLE CODE DEFINITIONS ("S" & "T" SERIES 4.3L VIN W)

HARD OR INTERMITTENT TROUBLE CODE DETERMINATION (GASOLINE)

During any diagnostic procedure, it must be determined if codes are hard failure codes or intermittent failure codes. Diagnostic charts will not usually help analyze intermittent codes. To determine hard codes and intermittent codes, proceed as follows

1) Enter diagnostic mode. See RETRIEVING CODES. Read and record all stored trouble codes. Exit diagnostic mode and clear trouble codes. See CLEARING TROUBLE CODES .

2) Apply parking brake and place transmission in Neutral or Park. Block drive wheels and start engine. MIL should go out. Run warm engine at specified curb idle for 2 minutes and note MIL.

3) If MIL comes on, enter diagnostic mode. Read and record DTCs. This will reveal hard failure codes. DTCs may require a road test to reset hard failure after clearing DTC. If MIL does not come on, all stored DTCs were intermittent failures.

CLEARING TROUBLE CODES

Note. To prevent PCM damage, ensure ignition switch is in OFF position when disconnecting or reconnecting power to PCM.

Diesel

To clear codes, use Tech 1 scan tester. If scan tester is not available, perform the following procedure. With ignition off, connect a jumper wire between Data Link Connector (DLC) terminal "B" (diagnostic terminal) and terminal "A" (ground). (Scheme 40) Turn ignition on. Fully apply brake pedal, then fully apply accelerator pedal. Check MIL for DTC 12. Release brake pedal, then release accelerator pedal. Check MIL again for DTC 12. Remove jumper wire from DLC. Turn ignition off.

Gasoline

Turn ignition switch to ON position, and ground diagnostic test terminal "B" at DLC connector. (Scheme 39) Turn ignition switch to OFF position, and remove control module fuse from fuse block for 30 seconds. Replace fuse. Remove diagnostic terminal ground lead. If fuse cannot be located, disconnect pigtail at battery. However, this may result in loss of other on-board memory data, such as preset radio tuning. After power to PCM is removed, poor driveability may occur until control module "relearns" operating parameters.

Diagnostic Charts

Following charts are DTC specific. For terminal locations, see WIRING DIAGRAMS . For engine-related DTCs, see appropriate TESTS W/CODES article in ENGINE PERFORMANCE section.

Diagnostic Aids

Diagnostic aids located in many trouble code charts are additional tips used to help diagnose trouble codes when circuit checks do not find a problem.

Note. In following diagnostic tests, schematics and illustrations are courtesy of General Motors Corp. Powertrain Control Module (PCM) may also be referred to as Electronic Control Module (ECM) or Transmission Control Module (TCM) in some diagnostic charts and figures. Terms are used interchangeably.

Circuit Description

CODE 14 PCM TERMINAL & CIRCUIT WIRING IDENTIFICATION

1. For shared sensor ground tie-offs, see appropriate wiring diagram in «WIRING DIAGRAMS»(/chevrolet/caprice-impala-ss/1995-1996/remont/automatic-trans/#diagnosis-4l60-e) .

Set Condition

Code will set if PCM sees an extremely high temperature signal (low voltage). Most likely causes of code are: sensor signal circuit shorted to ground, faulty coolant temperature sensor or faulty PCM.

Test Description

Note. This chart assumes engine cooling system is functioning properly (not overheating). Test numbers refer to numbers on diagnostic chart.

1. This checks if conditions for code still exist.
2. This tests for grounded sensor signal line between control module and coolant sensor.

Code 14, Circuit Diagram (Cars) Courtesy of General Motors Corp. Scheme 41

Code 14, Flow Chart (Cars) Courtesy of General Motors Corp. Scheme 42

After engine is started, temperature should rise steadily to about 194°F (90°C) and then stabilize when thermostat opens. At normal operating temperature, signal voltage at control module terminal should be 1.5-2.0 volts. Check sensor for shifted calibration by using sensor TEMPERATURE-TO-RESISTANCE VALUES table. When code is set, control module will turn on electric cooling fan(s) if equipped.

TEMPERATURE-TO-RESISTANCE VALUES

CODE 15, CTS SIGNAL VOLTAGE HIGH (LOW TEMPERATURE INDICATED)

CODE 15 PCM TERMINAL & CIRCUIT WIRING IDENTIFICATION

1. For shared sensor ground tie-offs, see appropriate wiring diagram in «WIRING DIAGRAMS»(/chevrolet/caprice-impala-ss/1995-1996/remont/automatic-trans/#diagnosis-4l60-e) .

Code indicates control module has seen high resistance (high monitored voltage) in coolant sensor circuit. This could be due to high resistance (cold temperature) or high voltage at coolant sensor terminal at control module for a precalibrated period of time. Most likely causes of code are: open sensor signal circuit, open sensor ground circuit (not allowing path to ground for 5-volt reference), faulty sensor connection, faulty sensor, faulty PCM connection or faulty PCM.

Note. Test numbers refer to numbers on diagnostic chart.

1. This checks if conditions for code still exist.
2. This test simulates a low voltage condition. If control module recognizes low voltage signal, scan tester will display greater than about 266°F (130°C). This indicates control module and wiring are not at fault.
3. This test determines if coolant sensor ground or signal circuit is open.

After engine is started, temperature should rise steadily to about 194°F (90°C) and then stabilize when thermostat opens. At normal operating temperature, signal voltage at control module terminal should be 1.5-2.0 volts. Check sensor for shifted calibration by using sensor TEMPERATURE-TO-RESISTANCE VALUES table. When code is set, control module will turn on electric cooling fan(s) if equipped.

Code 15, Flow Chart (Cars) Courtesy of General Motors Corp. Scheme 43

TEMPERATURE-TO-RESISTANCE VALUES

Code 21, Circuit Diagram (Cars) Courtesy of General Motors Corp. Scheme 44

CODE 21 PCM TERMINAL & CIRCUIT WIRING IDENTIFICATION

1. For shared sensor ground tie-offs, see appropriate wiring diagram in «WIRING DIAGRAMS»(/chevrolet/caprice-impala-ss/1995-1996/remont/automatic-trans/#diagnosis-4l60-e) .

Code will set if engine is idling (closed throttle), MAP value is low, a MAP code is not set and PCM sees high TP sensor voltage. Most likely causes for code are: TP sensor signal circuit shorted to voltage, open sensor ground circuit, faulty sensor connection, faulty TP sensor or faulty PCM.

Note. Test numbers refer to numbers on diagnostic chart.

1. This test checks if code is result of a hard failure or an intermittent condition.
2. This test simulates a low-voltage condition. If control module recognizes change of state, control module and wiring are okay.
3. This step isolates a faulty sensor, control module or open sensor ground circuit. If sensor ground is shared by another sensor, an accompanying code related to that sensor may exist.

A scan tester displays throttle position in volts. Closed throttle voltage should be low. Voltage should increase gradually to about 4.5 volts at a steady rate as throttle angle is increased.

Code 21, Flow Chart (Cars) Courtesy of General Motors Corp. Scheme 45

CODE 22, THROTTLE POSITION SENSOR SIGNAL VOLTAGE LOW

CODE 22 PCM TERMINAL & CIRCUIT WIRING IDENTIFICATION

1. For shared sensor ground tie-offs, see appropriate wiring diagram in «WIRING DIAGRAMS»(/chevrolet/caprice-impala-ss/1995-1996/remont/automatic-trans/#diagnosis-4l60-e) .

Code will set if engine is running and TP sensor voltage is lower than base idle voltage (auto zero voltage). Most likely causes of code are: TP sensor signal circuit open or shorted to ground, 5-volt reference open or shorted to ground (should also set other codes), faulty sensor connection, faulty sensor, faulty PCM connection or faulty PCM.

Note. Test numbers refer to numbers on diagnostic chart.

1. This test checks if code is result of a hard failure or an intermittent condition.
2. This test simulates high voltage conditions. If control module recognizes change of state, control module and wiring are okay.
3. This simulates a high signal voltage to check for an open in TP sensor signal line to control module. Scan tester should recognize this signal and display high TP sensor voltage.

A scan tester displays throttle position in volts. Closed throttle voltage should be low. Voltage should increase gradually to about 4.5 volts at a steady rate as throttle angle is increased.

Code 22, Flow Chart (Cars) Courtesy of General Motors Corp. Scheme 46

Code 24, Circuit Diagram (3.4L F Body) Courtesy of General Motors Corp. Scheme 47

Code 24, Circuit Diagram (4.3L & 5.7L B Body) Courtesy of General Motors Corp. Scheme 48

Code 24, Circuit Diagram (5.7L D Body) Courtesy of General Motors Corp. Scheme 49

Code 24, Circuit Diagram (5.7L F Body) Courtesy of General Motors Corp. Scheme 50

Code 24, Circuit Diagram (5.7L Y Body) Courtesy of General Motors Corp. Scheme 51

Speed sensor, which is a Permanent Magnet (PM) generator, provides control module with vehicle speed information. PM generator, mounted in transmission, produces a pulsing AC voltage signal whenever vehicle speed is greater than about 2 MPH. Voltage level and pulses increase with vehicle speed. Control module converts pulsing voltage to MPH, which is used by control module to calculate vehicle adjustments.

Note. Test numbers refer to numbers on diagnostic chart.

Note. Prior to testing Corvette for Code 24, disable Acceleration Slip Regulation (ASR) system.

1. PM generator only produces a voltage signal if drive wheels are turning greater than about 2 MPH.

A faulty or misadjusted park/neutral switch may set a false Code 24. Use scan tester to check for proper signal in Drive while wiggling shifter. Code 24 may set if vehicle is power braked (brakes applied and throttle depressed) for more than 10 seconds.

Code 24, Flow Chart (Cars) Courtesy of General Motors Corp. Scheme 52

Code 28, Circuit Diagram (3.4L F Body) Courtesy of General Motors Corp. Scheme 53

Code 28, Circuit Diagram (4.3L & 5.7L B Body) Courtesy of General Motors Corp. Scheme 54

Code 28, Circuit Diagram (5.7L D Body) Courtesy of General Motors Corp. Scheme 55

Code 28, Circuit Diagram (5.7L F Body) Courtesy of General Motors Corp. Scheme 56

Code 28, Circuit Diagram (5.7L Y Body) Courtesy of General Motors Corp. Scheme 57

Transmission range pressure switch assembly consists of 5 pressure switches (2 normally closed, 3 normally open), and a fluid temperature sensor combined into one unit and mounted on the valve body. PCM supplies voltage to each range signal. By grounding one or more of these circuits through various combinations of pressure switches, PCM detects which manual valve position has been selected. With ignition on and engine off, Park/Neutral will be indicated. Code 28 will set when range signals "A" and "C" are both zero volts (on) for 2 seconds.

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks indicated range signal to valve position signal actually selected.
2. Checks for correct voltage from PCM to transmission external connector.
3. Checks for short to ground in any one of the 3 valve position circuits.

Code will set if PCM detects one of 2 illegal combinations. Check all connections for good contact.

Code 28, Flow Chart (Cars). Scheme 58

Code 37, Circuit Diagram (3.4L F Body) Courtesy of General Motors Corp. Scheme 59

Code 37, Circuit Diagram (4.3L & 5.7L B & Y Bodies) Courtesy of General Motors Corp. Scheme 60

Code 37, Circuit Diagram (5.7L D Body) Courtesy of General Motors Corp. Scheme 61

Code 37, Circuit Diagram (5.7L F Body) Courtesy of General Motors Corp. Scheme 62

PCM monitors activity of the normally-closed brake switch. Switch opens when brake pedal is applied.

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks for voltage at brake switch.
2. Simulates brake switch closed or brakes off.
3. Checks TCC brake switch circuit between PCM and switch.

Code 37 can be caused by a misadjusted brake switch or a poor connection. Code may also be set by unusual driving habits (i.e. stop-and-go expressway driving).

Code 37, Flow Chart (Cars) Courtesy of General Motors Corp. Scheme 63

CODE 38, BRAKE SWITCH ERROR - 4.3L & 5.7L "B/D/F/Y" BODIES

PCM monitors activity of the normally-closed brake switch. Switch opens when brake pedal is applied. Code will set if PCM has seen conditions which would have required brake applications at least 7 times and no transition in brake switch has been detected.

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks for voltage at brake switch.
2. Simulates brake switch closed or brakes off. Checks brake switch circuit between PCM and switch.
3. Checks circuit between brake switch and PCM.

Code may also be set by unusual driving habits (i.e. stop-and-go expressway driving).

Code 38, Flow Chart (Cars) Courtesy of General Motors Corp. Scheme 64

Code 53, Circuit Diagram (3.4L F Body) Courtesy of General Motors Corp. Scheme 65

Code 53, Circuit Diagram (4.3L & 5.7L B & D Bodies) Courtesy of General Motors Corp. Scheme 66

Code 53, Circuit Diagram (5.7L F Body) Courtesy of General Motors Corp. Scheme 67

Code 53, Circuit Diagram (5.7L Y Body) Courtesy of General Motors Corp. Scheme 68

This code indicates a basic charging system problem. Code 53 will set when voltage at control module terminal is greater than specification for a precalibrated time. If voltage at PCM battery voltage terminal is not within specification, check and repair charging system.

Code 53, Flow Chart (Cars) Courtesy of General Motors Corp. Scheme 69

CHARGING SYSTEM SPECIFICATIONS

CODE 58, TRANS. TEMP. SENSOR HIGH - 3.4L "F" BODY, 4.3L & 5.7L "B", "D", "F" & "Y" BODIES

Temperature sensor is a 2 wire thermistor located in transaxle. This sensor operates in the same manner as engine coolant temperature sensor and intake air temperature sensor. PCM applies 5 volts to sensor on signal circuit. Voltage sensed at PCM signal circuit terminal will be high when transmission fluid is cold and as fluid warms voltage signal will drop. A very low signal voltage indicates a high fluid temperature or a failure in sensor circuit. Normal fluid temperature range is 167-212°F (75-100°C).

Code 58 will set when sensor indicates a high fluid temperature for a precalibrated period of time. Malfunction Indicator Light (MIL) will illuminate and PCM will use a warm default sensor value.

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks for a short to ground or an out-of-calibration sensor.
2. Checks for an internal fault within the transmission by creating an open.

Check harness routing for a potential short to ground in signal circuit. Temperature should rise steadily to about 194°F (90°C) then stabilize. A skewed sensor could result in delayed shifts or TCC enabled complaints.

Use temperature-to-resistance table to check sensor at various levels to determine if sensor is out-of-calibration, which could result in firm shifts or TCC enable.

Code 58, Flow Chart (Cars) Courtesy of General Motors Corp. Scheme 70

TEMPERATURE-TO-RESISTANCE VALUES

CODE 59, TRANS. TEMPERATURE SENSOR LOW TEMPERATURE - 3.4L "F" BODY, 4.3L & 5.7L "B", "D", "F" & "Y" BODIES

Temperature sensor is a 2 wire thermistor located in transaxle. This sensor operates in the same manner as engine coolant temperature sensor and intake air temperature sensor. PCM applies 5 volts to sensor on signal circuit. Voltage sensed at PCM signal circuit terminal will be high when transmission fluid is cold and as fluid warms voltage signal will drop. A very high signal voltage indicates a low fluid temperature or a failure in sensor circuit. Normal fluid temperature range is 167-212°F (75-100°C).

Code 59 will set when sensor indicates a low temperature for a precalibrated period of time. Malfunction Indicator Light (MIL) will not illuminate and PCM will use a warm default sensor value.

Note. Test numbers refer to numbers on diagnostic chart.

1. This test determines if a current condition exists.
2. Simulates a Code 58. If PCM recognizes low signal voltage, and scan displays about 295°F (146°C) or higher, PCM and wiring are okay.
3. Checks if signal circuit is open. Five volts should be present at sensor connector.

Temperature should rise steadily to about 194°F (90°C), then stabilize. A faulty connection or an open in ground or signal circuit can result in Code 59. A skewed sensor could result in firm shifts or TCC enabled complaints.

Use temperature-to-resistance table to check sensor at various levels to determine if sensor is out-of-calibration, which could result in firm shifts or TCC enable.

Code 59, Flow Chart (Cars) Courtesy of General Motors Corp. Scheme 71

TEMPERATURE-TO-RESISTANCE VALUES

Code 72, Flow Chart (B, F & D Bodies) Courtesy of General Motors Corp. Scheme 72

Speed sensor, which is a Permanent Magnet (PM) generator, provides control module with vehicle speed information. PM generator, mounted in transmission, produces a pulsing AC voltage signal whenever vehicle speed is greater than about 2 MPH. Voltage level and pulses increase with vehicle speed. Control module converts pulsing voltage to MPH, which is used by control module to calculate vehicle adjustments.

Note. Test numbers refer to numbers on diagnostic chart.

1. An intermittent connection at VSS or PCM may cause code to set. Inspect harness and all related connections. Check for damage or pushed out terminals.
2. Ensure harness is routed away from hot exhaust components.
3. If software/calibration is incorrect, code will set. Ensure calibration is correct before replacing PCM.

CODE 72, VEHICLE SPEED SENSOR LOSS - 5.7L "Y" BODY

Speed sensor is a PM generator located on transmission output shaft.

Note. Test numbers refer to numbers on diagnostic chart.

1. Disable TC system (if equipped) when performing this step. Whenever ignition is cycled to off position and then back to on, TC system will default on. An intermittent connection at VSS or PCM may cause code to set. Inspect harness and all related connections. Check for damage or pushed out terminals. Prior to replacing PCM, check for correct software calibration (reprogrammable).

Code 72 will set when vehicle speed has been detected and then lost.

Code 73, Circuit Diagram (Cars) Courtesy of General Motors Corp. Scheme 73

Pressure control solenoid is a PCM-controlled device used to regulate transmission line pressure. PCM compares TPS voltage, engine RPM and other inputs to determine proper line pressure for a given load. PCM regulates pressure by applying a varying amperage to pressure control solenoid. Amperage varies from 0.1 to 1.1 amps.

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks ability of the PCM to command pressure control solenoid.
2. Checks for voltage at PCM.

Check for poor connections at PCM and at transmission connector.

Code 73, Flow Chart (Cars) Courtesy of General Motors Corp. Scheme 74

Code 74, Circuit Diagram (Cars) Courtesy of General Motors Corp. Scheme 75

PCM monitors traction control system activity (battery voltage input signal) and inhibit upshifts, downshifts and TCC operation during system activity (zero volts on signal line).

Note. Test numbers refer to numbers on diagnostic chart.

1. If fault exists, scan tester will display TCS activity. A short to ground in an external component or wiring could be the cause for setting of code.

Check related harness connectors, including PCM harness. Check for damaged or pushed out terminals. Wiggle harness while monitoring scan tester TCS status. If status changes, wiring is faulty.

Code 74, Flow Chart (Cars) Courtesy of General Motors Corp. Scheme 76

Code 75, Circuit Diagram (Cars) Courtesy of General Motors Corp. Scheme 77

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks for normal battery voltage of 9-15 volts.
2. Checks if low voltage is due to generator voltage supply circuit, or PCM. If voltage is less than 9 volts, PCM is okay.

If code sets when an accessory is operated, check for poor connections or excessive current draw. Also, check for poor connections at starter solenoid or fusible link.

Code 75, Flow Chart (Cars) Courtesy of General Motors Corp. Scheme 78

CODE 79, TRANSMISSION FLUID OVERTEMP - 3.4L "F" BODY, 4.3L & 5.7L "B", "D", "F" & "Y" BODIES

PCM supplies and monitors a 5-volt reference to sensor. As transmission temperature changes, sensor resistance changes, affecting monitored voltage. When fluid is cold, resistance is high, resulting in a high monitored voltage. When fluid is hot, resistance is low, resulting in a low monitored voltage. Code will set if transmission temperature is 248-266°F (120-130°C) for 5 seconds and Codes 58 and 59 are not set.

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks for out-of-calibration sensor or shorted circuit.
2. Simulates Code 59.

Check harness for potential short to ground. See Code 59 chart to check transmission temperature sensor temperature-to-resistance values. Also, check transmission fluid level. Check for conditions which could cause transmission to overheat i.e. trailer towing, steep grades, etc.

Code 79, Flow Chart (Cars) Courtesy of General Motors Corp. Scheme 79

TEMPERATURE-TO-RESISTANCE VALUES

Code 80, Circuit Diagram (Cars) Courtesy of General Motors Corp. Scheme 80

PCM monitors difference between engine speed and transmission input shaft speed. With selector in D3 or D4 (indicated gear 2, 3 or 4), and TCC is locked, scan should display engine speed closely matching input speed.

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks indicated range signal to the actual selected range.
2. Checks torque converter for slippage while in a commanded locked-up state.

Check for poor connections at pass-through connector. A faulty transmission range pressure switch assembly may set Code 80.

Code 80, Flow Chart (Cars) Courtesy of General Motors Corp. Scheme 81

Code 81, Circuit Diagram (4.3L & 5.7L B & F Bodies) Courtesy of General Motors Corp. Scheme 82

Code 81, Circuit Diagram (5.7L D Body) Courtesy of General Motors Corp. Scheme 83

Code 81, Circuit Diagram (5.7L Y Body) Courtesy of General Motors Corp. Scheme 84

Voltage is supplied directly to solenoid. PCM controls solenoid by providing a ground circuit.

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks 2-3 shift solenoid and internal transmission for shorts.
2. Checks for power to 2-3 shift solenoid from ignition through the fuse.

Check all connections at the transmission. An open in ignition feed circuit can cause multiple codes to set.

Code 81, Flow Chart (Cars) Courtesy of General Motors Corp. Scheme 85

Code 82, Circuit Diagram (4.3L & 5.7L B Bodies) Courtesy of General Motors Corp. Scheme 86

Code 82, Circuit Diagram (5.7L D Body) Courtesy of General Motors Corp. Scheme 87

Code 82, Circuit Diagram (5.7L F Body) Courtesy of General Motors Corp. Scheme 88

Code 82, Circuit Diagram (5.7L Y Body) Courtesy of General Motors Corp. Scheme 89

Voltage is supplied directly to solenoid. PCM controls solenoid by providing a ground circuit for solenoid.

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks 1-2 shift solenoid and internal transmission for shorts.
2. Checks for power to 1-2 shift solenoid from ignition through the fuse.

Check all connections at the transmission. An open in ignition feed circuit can cause multiple codes to set.

Code 82, Flow Chart (Cars) Courtesy of General Motors Corp. Scheme 90

Code 83, Circuit Diagram (4.3L & 5.7L B & F Bodies) Courtesy of General Motors Corp. Scheme 91

Code 83, Circuit Diagram (5.7L D Body) Courtesy of General Motors Corp. Scheme 92

Code 83, Circuit Diagram (5.7L Y Body) Courtesy of General Motors Corp. Scheme 93

PCM controls and monitors TCC PWM solenoid drive circuit. If voltage remains high when solenoid is commanded on or remains low when commanded off, code will set.

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks if PCM is commanding TCC solenoid on.
2. Checks for voltage to solenoid.

Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wire connections or damaged harness.

Perform intermittent check by monitoring circuit and code status while wiggling related wiring and connectors. If failure is induced, monitored circuit status will change rapidly and/or related code will set.

Code 83, Flow Chart (Cars) Courtesy of General Motors Corp. Scheme 94

Code 84, Circuit Diagram (4.3L & 5.7L B Body) Courtesy of General Motors Corp. Scheme 95

Code 84, Circuit Diagram (5.7L D Body) Courtesy of General Motors Corp. Scheme 96

Code 84, Circuit Diagram (5.7L F Body) Courtesy of General Motors Corp. Scheme 97

Code 84, Circuit Diagram (5.7L Y Body) Courtesy of General Motors Corp. Scheme 98

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks 3-2 shift solenoid and internal transmission harness for shorts.
2. Checks for power to 3-2 shift solenoid from ignition through the fuse.

Check all connections at the transmission. An open in ignition feed circuit can cause multiple codes to set.

Code 84, Flow Chart (Cars) Courtesy of General Motors Corp. Scheme 99

Code 85, Circuit Diagram (Cars) Courtesy of General Motors Corp. Scheme 100

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks mechanical state of TCC when PCM commands TCC solenoid off. TCC slip speed should increase.

Check for proper TP sensor operation. If TCC is mechanically stuck on, vehicle speed is zero, brakes are applied, and D2 is selected, TCC fluid will mechanically apply the TCC, causing an engine stall.

Code 85, Flow Chart (Cars) Courtesy of General Motors Corp. Scheme 101

Code 90, Circuit Diagram (3.4L F Body) Courtesy of General Motors Corp. Scheme 102

Code 90, Circuit Diagram (4.3L & 5.7L B, D, F & Y Bodies) Courtesy of General Motors Corp. Scheme 103

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks for a shorted internal transmission harness or TCC solenoid.
2. Checks power supply to TCC solenoid.

Check all connections to transmission pass-through connector. An open in the ignition feed circuit will cause multiple codes to set.

Code 90, Flow Chart (Cars) Courtesy of General Motors Corp. Scheme 104

Code 93, Circuit Diagram (Cars) Courtesy of General Motors Corp. Scheme 105

Pressure control solenoid is a PCM-controlled device used to regulate transmission line pressure. PCM compares TPS voltage, engine RPM and other inputs to determine proper line pressure for a given load. PCM regulates pressure by applying a varying amperage to pressure control solenoid. Amperage varies from 0.1 to 1.1 amps.

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks ability of PCM to command pressure control solenoid.
2. Checks for voltage at PCM.

Check for poor connections at PCM and at transmission connector.

Code 93, Flow Chart (Cars) Courtesy of General Motors Corp. Scheme 106

CODE 96, TRANSMISSION VOLTAGE LOW - 3.4L "F" BODY

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks for normal battery voltage of 9-15 volts.
2. Checks if low voltage is due to generator voltage supply circuit, or PCM. If voltage is less than 9 volts, PCM is okay.

If code sets when an accessory is operated, check for poor connections or excessive current draw. Also, check for poor connections at starter solenoid or fusible link.

Following charts are DTC specific. For terminal locations, see WIRING DIAGRAMS . For engine-related DTCs, see appropriate TESTS W/CODES article in ENGINE PERFORMANCE section.

Diagnostic aids located in many trouble code charts are additional tips used to help diagnose trouble codes when circuit checks do not find a problem.

Note. In following diagnostic tests, schematics and illustrations are courtesy of General Motors Corp. Powertrain Control Module (PCM) may also be referred to as Electronic Control Module (ECM) or Transmission Control Module (TCM) in some diagnostic charts and figures. Terms are used interchangeably.

CODE 14, COOLANT TEMPERATURE SENSOR SIGNAL VOLTAGE LOW

CODE 14 TERMINAL & CIRCUIT WIRING IDENTIFICATION

Coolant temperature sensor input is used to determine control of fuel delivery, engine timing, idle speed and converter clutch (TCC) application. As engine warms, sensor resistance reduces. At normal operating temperature, voltage signal will be about 1.5-2.0 volts at coolant sensor signal terminal.

Note. Test numbers refer to test numbers on diagnostic chart.

1. This tests if code was set because of a hard failure or intermittent condition.
2. This simulates conditions for a Code 15. If scan tester displays a low temperature, control module and wiring are not at fault.

After engine is started, temperature should rise steadily to about 194°F (90°C), then stabilize when thermostat opens. Test sensor at various temperature levels to determine if sensor is out of calibration. See TEMPERATURE-TO-RESISTANCE VALUES chart. If engine is allowed to cool overnight, coolant temperature sensor and intake air temperature sensor (if equipped) should read close to each other, when measured with a scan tester.

TEMPERATURE-TO-RESISTANCE VALUES

CODE 15, COOLANT TEMPERATURE SENSOR SIGNAL VOLTAGE HIGH

CODE 15 TERMINAL & CIRCUIT WIRING IDENTIFICATION

As engine warms, sensor resistance reduces and voltage drops. At normal operating temperature, voltage signal will be about 1.5-2.0 volts at control module coolant sensor signal terminal. If sensor signal circuit opens, control module will see -56°F (-49°C) and deliver fuel for this temperature.

Note. Test numbers refer to test numbers on diagnostic chart.

1. This checks if code was set as a result of a hard failure or intermittent condition.
2. This simulates conditions for a Code 14. If control module recognizes grounded circuit and displays a high temperature, control module and wiring are okay.
3. This determines if problem is control module or wiring. There should be 5 volts present at sensor when measured with a DVOM.

After engine starts, temperature should rise steadily to about 194°F (90°C) and stabilize when thermostat opens. Test sensor at various temperature levels to determine if sensor is out of calibration. See the TEMPERATURE-TO-RESISTANCE VALUES chart. If engine is allowed to cool overnight, coolant temperature sensor and intake air temperature sensor (if equipped) should read close to each other when measured with a scan tester. Code 15 will also set if sensor signal or ground circuit is open.

TEMPERATURE-TO-RESISTANCE VALUES

CODE 21, TPS SIGNAL VOLTAGE HIGH

CODE 21 TERMINAL & CIRCUIT WIRING IDENTIFICATION

Throttle Position Sensor (TPS) provides a varying voltage signal depending on throttle valve angle. Signal voltage varies from about .50 volt at idle to 4 volts at wide open throttle. Each time TPS voltage drops to less than 1.25 volts and stops, control module assumes this is zero degrees throttle angle and measures throttle percentage angle from this point.

Note. Test numbers refer to test numbers on diagnostic chart.

1. This test confirms Code 21 and checks if fault is a hard failure or an intermittent condition.
2. This test simulates conditions for Code 22. If control module recognizes low voltage signal and sets Code 22, control module and power and signal circuits are not at fault.
3. This step isolates a faulty sensor, control module or an open ground circuit.

A scan tester displays throttle position in volts. Closed throttle voltage should be less than 1.25 volts. TPS voltage should increase at a steady rate to about 4.5 volts as throttle angle increases. Code 21 will also result if ground circuit is open or TPS signal circuit is shorted to voltage.

Code 21, Flow Chart (Trucks & Vans) Courtesy of General Motors Corp. Scheme 107

CODE 22, TPS SIGNAL VOLTAGE LOW

CODE 22 TERMINAL & CIRCUIT WIRING IDENTIFICATION

Throttle Position Sensor (TPS) provides a varying voltage signal depending on throttle valve angle. Signal voltage varies from less than about .50 volt at idle to 4 volts at wide open throttle.

Note. Test numbers refer to test numbers on diagnostic chart.

1. This test confirms Code 22 and tests if fault is a hard failure or an intermittent condition.
2. This simulates Code 21. If control module recognizes a high voltage signal and sets Code 21, control module and wiring are not at fault. Replace TPS.
3. This simulates a high voltage signal to check for on open TPS signal circuit.

A scan tester displays throttle position in volts. Closed throttle voltage should be less than 1.0 volt. TPS voltage should increase at a steady rate to about 4.5 volts as throttle angle increases. Code 22 will also set if TPS signal or ground circuits are open or grounded.

Code 24, Circuit Diagram (C & K Series) Courtesy of General Motors Corp. Scheme 108

Code 24, Circuit Diagram (G Series) Courtesy of General Motors Corp. Scheme 109

Code 24, Circuit Diagram (L & M Series) Courtesy of General Motors Corp. Scheme 110

Code 24, Circuit Diagram (S & T Series) Courtesy of General Motors Corp. Scheme 111

VSS output sensor is a magnetic induction type. Gear teeth pressed on outside diameter of output carrier assembly induce an alternating current in sensor when drive wheels are turning. Since vehicle speed is taken from transfer case on 4WD vehicles, output speed sensor signal on these units goes directly to control module. Code 24 will set if gear selector is not in Park or Neutral, engine speed is at least 3000 RPM and output speed is less than 250 RPM for at least 1.5 seconds.

Note. Test numbers refer to test numbers on diagnostic chart.

1. Test verifies voltage at buffer module.
2. Test checks VSS buffer ground circuit.
3. Test checks VSS circuit at buffer module.
4. Test verifies VSS signal at from module.

Code 24 will set when no vehicle speed is detected at vehicle start off. Code 72 will set when VSS signal is present and is lost. Check all connections, especially those at transmission pass-through connector. While Code 24 is set, scan tester will display an RPM derived from input speed. If input speed sensor is not operational at start-up, this can cause VSS to read zero.

Code 24, Flow Chart (Trucks & Vans) Courtesy of General Motors Corp. Scheme 112

Code 28, Circuit Diagram (C & K Series) Courtesy of General Motors Corp. Scheme 113

Code 28, Circuit Diagram (G, L, M, S & T Series) Courtesy of General Motors Corp. Scheme 114

Transmission range pressure switch assembly consists of 5 pressure switches (2 normally closed, 3 normally open), and a fluid temperature sensor combined into one unit and mounted on valve body. Control module supplies voltage to each range signal. By grounding one or more of these circuits through various combinations of pressure switches, control module detects which manual valve position has been selected. With ignition on and engine off, Park/Neutral will be indicated. Code 28 will set when range signals "A" and "C" are both zero volts (on) for 2 seconds.

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks indicated range signal to valve position signal actually selected.
2. Checks for correct voltage from control module to transmission external connector.
3. Checks for short to ground in any one of 3 valve position circuits.

Code will set if control module detects one of 2 illegal combinations. Check all connections for good contact. An intermittent may be caused by a poor connection, chaffed wire insulation or a broken wire. Monitor voltage of each terminal while moving related harness connectors. If failure is induced, voltage reading will change.

VALID PSM COMBINATION

Code 37/38, Circuit Diagram (C, G & K Series) Courtesy of General Motors Corp. Scheme 115

Code 37/38, Circuit Diagram (L, M, S & T Series) Courtesy of General Motors Corp. Scheme 116

The normally closed brake switch supplies battery voltage to control module. Signal voltage will drop to zero volts when brake pedal is applied.

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks if voltage is available at brake switch.
2. Checks brake switch function.
3. Checks circuit from brake switch to control module.

If code is intermittent, check customer driving habits (driving with foot resting on brake pedal) or for unusual traffic conditions (stop and go expressway traffic).

Code 52/53, Circuit Diagram (C & K Series) Courtesy of General Motors Corp. Scheme 117

Code 52/53, Circuit Diagram (G, L & M Series) Courtesy of General Motors Corp. Scheme 118

Code 52/53, Circuit Diagram (S & T Series) Courtesy of General Motors Corp. Scheme 119

Code 53 will set when ignition is on and control module 12-volt battery feed voltage is greater than 19.5 volts for about 2 seconds. During the time failure is present, force motor is turned off, transmission immediately shifts to 2nd gear, and TCC operation is inhibited. The setting of additional codes may result.

Note. Test numbers refer to test numbers on diagnostic chart.

1. Normal voltage is 9-15 volts.
2. Checks if alternator is faulty under load.

Jump-starting engine or charging battery with a battery charger may set code. If code is set when an accessory is operated, check for poor connections or excessive current draw. Also, check for poor connections at starter solenoid or fusible link.

Code 52/53, Flow Chart (Trucks & Vans) Courtesy of General Motors Corp. Scheme 120

Code 58, Circuit Diagram (C & K Series) Courtesy of General Motors Corp. Scheme 121

Code 58, Circuit Diagram (G, L, M, S & T Series) Courtesy of General Motors Corp. Scheme 122

Transmission fluid temperature sensor is a thermistor which controls signal voltage to control module. Control module applies and monitors voltage to sensor. When transmission fluid is cold, sensor resistance is high; therefore, control module will see high signal voltage. As transmission fluid warms, sensor resistance and voltage will drop. At normal transmission operating temperature of 212°F (100°C), voltage will be about 1.5-2.0 volts.

Note. Test numbers refer to numbers on diagnostic chart.

1. Code 58 will set if signal voltage indicates a transmission fluid temperature greater than 305°F (151°C) for one second.
2. This test determines if circuit is shorted to ground, which will result in conditions for Code 58.

Check harness routing for a potential short to ground in TFT signal circuit. Scan tester displays transmission fluid temperature in degrees Centigrade. After transmission is running, temperature display should rise steadily to about 212°F (100°C) then stabilize. Test transmission sensor at various temperature levels to determine if sensor is out of calibration. See TEMPERATURE-TO-RESISTANCE VALUES chart. An out-of-calibration sensor could result in delayed shifts or TCC enabled complaint.

TEMPERATURE-TO-RESISTANCE VALUES

CODE 59, TRANS. FLUID TEMP. LOW

Transmission fluid temperature sensor is a thermistor which controls signal voltage to control module. Control module applies and monitors 5 volts to sensor. When transmission fluid is cold, sensor resistance is high; therefore, control module will see high signal voltage. As transmission fluid temperature warms, sensor resistance and voltage drop. At normal transmission operating temperature of 212°F (100°C), voltage will be about 1.5-2.0 volts.

Note. Test numbers refer to numbers on diagnostic chart.

1. Code 59 will set if signal voltage indicates a transmission fluid temperature less than -34°F (-37°C) for one second.
2. This test simulates Code 58. If control module recognizes low signal voltage (high temperature) and scan tester reads 305°F (151°C) or greater, control module and wiring are okay.
3. This test determines if signal circuit is open. There should be 5 volts present at sensor connector if measuring with a DVOM.

Scan tester displays transmission fluid temperature in degrees Centigrade. After transmission is running, displayed temperature should rise steadily to about 212°F (100°C) then stabilize. A faulty connection or an open in ground circuit or signal circuit will result in a Code 59. Test transmission sensor at various temperature levels to determine if sensor is out of calibration. See TEMPERATURE-TO-RESISTANCE VALUES. An out-of-calibration sensor could result in firm shifts or TCC enabled complaint.

TEMPERATURE-TO-RESISTANCE VALUES

Code 66, Circuit Diagram (Trucks & Vans) Courtesy of General Motors Corp. Scheme 123

The 3-2 control solenoid hydraulically coordinates apply rate of 2-4 band with hydraulic release of 3-4 clutch during a 3-2 downshift. The 3-2 circuit duty cycle is continually monitored by control module depending one command state of circuit. When transmission is in 1st gear, duty cycle of solenoid is equal to zero. When transmission is in 2nd gear or higher, duty cycle of solenoid will be about 90 percent. When transmission downshifts 3-2, duty cycle of solenoid will be about 20 percent.

Note. Test numbers refer to numbers on diagnostic chart.

1. This test checks 3-2 control solenoid and internal transmission harness for short circuits.
2. This test checks for power, from ignition through fuse, to 3-2 control solenoid.

Check all connections, especially those at transmission pass-thru connector. Some slight TCC slippage is normal. The 3-2 control solenoid feedback normally oscillates on/off when duty cycle is applied.

Code 67, Circuit Diagram (Trucks & Vans) Courtesy of General Motors Corp. Scheme 124

TCC solenoid is a normally open exhaust valve. Control module will engage solenoid by grounding circuit with an internal quad-driver.

Note. Test numbers refer to numbers on diagnostic chart.

1. This test checks ability of control module to control solenoid.
2. This test checks for power, from ignition through fuse, to TCC solenoid.

Check all connections, especially those at transmission pass-thru connector. Some slight TCC slippage is normal.

Code 69, Circuit Diagram (Trucks & Vans) Courtesy of General Motors Corp. Scheme 125

Control module commands TCC PWM solenoid on by modulating signal fluid on converter clutch shift valve. TCC apply fluid applies torque converter clutch.

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks mechanical state of TCC. When TCC is commanded off, slip speed should increase.

If TCC is mechanically stuck on, TCC fluid will apply TCC, causing an engine stall.

Code 72, Circuit Diagram (C, G, K, L & M Series) Courtesy of General Motors Corp. Scheme 126

Code 72, Circuit Diagram (S & T Series) Courtesy of General Motors Corp. Scheme 127

VSS output sensor is a magnetic induction type. Gear teeth pressed on outside diameter of output carrier assembly induce an alternating current in sensor when drive wheels are turning.

Note. Test numbers refer to test numbers on diagnostic chart.

1. Test verifies VSS voltage at control module.
2. Test checks VSS buffer ground circuit.
3. Test checks VSS circuit at buffer module.
4. Test verifies VSS signal at sensor.

Code 72 will set when VSS signal is present and is lost. Code 24 will set when no vehicle speed is detected at vehicle start off. Check all connections, especially those at transmission pass-through connector.

Code 72, Flow Chart (Trucks & Vans) Courtesy of General Motors Corp. Scheme 128

Code 73, Circuit Diagram (Trucks & Vans) Courtesy of General Motors Corp. Scheme 129

Note. This flow chart requires the use of a bidirectional (Tech 1) scan tester.

Pressure control solenoid is controlled by control module to regulate transmission line pressure. Control module looks at TPS voltage, engine RPM and other inputs to determine appropriate line pressure for a given load, then regulates pressure by applying a varying amperage. Applied amperage can vary from 1 to 1.1 amps. Control module then monitors amperage at return line.

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks ability of control module to command solenoid.
2. Checks internal transmission harness and solenoid for incorrect resistance.

Check for poor connections at control module and transmission pass-thru connector.

Scheme 130

Code 75, Circuit Diagram (Trucks & Vans) Courtesy of General Motors Corp. Scheme 131

Code 75 will set when ignition is on and control module 12-volt battery feed voltage is less than 9 volts for about 4 seconds. During time failure is present, force motor, also referred to as pressure control solenoid, is turned off, maintaining only 2nd gear and inhibiting TCC operation.

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks for normal battery voltage.
2. Checks if low voltage display is due to generator, battery voltage input circuit or control module.

Charging battery with a charger and jump starting engine may set this code. If code sets when an accessory is operated, check for poor connections or excessive current draw. Also, check for poor connections at starter solenoid or fusible link. Minimum voltage allowed for Code 75 to set is on a graduated scale and changes with temperature from a low of 7.3 volts at -40°F (-40°C) to a voltage of 11.7 volts at 304°F (150°C).

CODE 79, TRANS. FLUID TEMPERATURE HIGH

Transmission fluid temperature sensor is a thermistor which controls signal voltage to control module. Control module applies and monitors voltage to sensor. When transmission fluid is cold, sensor resistance is high; therefore, control module will see high signal voltage. As transmission fluid warms, sensor resistance and voltage will drop. At normal transmission operating temperature of 212°F (100°C), voltage will be about 1.5-2.0 volts.

Note. Test numbers refer to numbers on diagnostic chart.

1. Code 79 will set if signal voltage indicates a transmission fluid temperature greater than 151°C for one second.
2. This test determines if circuit is shorted to ground, which will result in conditions for Code 79.

Check harness routing for a potential short to ground in signal circuit. Scan tester displays transmission fluid temperature in degrees Centigrade. After transmission is running, temperature display should rise steadily to about 212°F (100°C) then stabilize. Test transmission sensor at various temperature levels to determine if sensor is out of calibration. See TEMPERATURE-TO-RESISTANCE VALUES chart. An out-of-calibration sensor could result in delayed shifts or TCC enabled complaint.

TEMPERATURE-TO-RESISTANCE VALUES

Code 81, Circuit Diagram (Trucks & Vans) Courtesy of General Motors Corp. Scheme 132

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks function of 2-3 shift solenoid and internal transmission wiring.
2. Checks for power to 2-3 shift solenoid from ignition.

Check all connections, especially those at transmission pass-thru connector.

Code 82, Circuit Diagram (Trucks & Vans) Courtesy of General Motors Corp. Scheme 133

Note. Test numbers refer to numbers on diagnostic chart.

1. This test checks 1-2 shift solenoid and internal transmission wiring harness for short circuits.
2. This test checks for power, from ignition through fuse, to shift solenoid.

Check all connections, especially at transmission pass-thru connector.

Code 83, Circuit Diagram (Trucks & Vans) Courtesy of General Motors Corp. Scheme 134

Control module continually monitors voltage on each circuit connected to quad-driver for either low or high voltage, depending on commanded state of device connected to it. Code 83 will set if control module detects an inappropriate reading on TCC circuit. For example, if TCC duty cycle is zero, but voltage on TCC circuit drops as if solenoid were on, then Code 83 will set. TCC solenoid, because of its large current draw, is connected to 2 terminals of a single quad-driver.

Note. Test numbers refer to numbers on diagnostic chart.

1. This test checks if control module is commanding TCC solenoid on.
2. This test checks for voltage to solenoid.

Check all connections, especially those at transmission pass-thru connector.

Following charts are DTC specific. For terminal locations, see WIRING DIAGRAMS . For engine-related DTCs, see appropriate TESTS W/CODES article in ENGINE PERFORMANCE section.

Diagnostic aids located in many trouble code charts are additional tips used to help diagnose trouble codes when circuit checks do not find a problem.

Note. In following diagnostic tests, schematics and illustrations are courtesy of General Motors Corp. Powertrain Control Module (PCM) may also be referred to as Electronic Control Module (ECM) or Transmission Control Module (TCM) in some diagnostic charts and figures. Terms are used interchangeably.

On-Board Diagnostic System Circuit Diagram (C & K Series Diesel) Courtesy of General Motors Corp. Scheme 135

On-Board Diagnostic System Circuit Diagram (G Series Diesel) Courtesy of General Motors Corp. Scheme 136

The On-Board Diagnostic (OBD) system check is an organized approach to identifying a problem created by a control module system malfunction. This is the starting point for any driveability complaint diagnosis, as it directs technician to the next logical step in diagnosis, helps reduce diagnostic time and prevents the unnecessary replacement of good parts.

Note. Test numbers refer to numbers on diagnostic chart.

1. This tests MIL operation. With ignition on and engine off, light should be on.
2. This step will isolate if customer complaint is a MIL or driveability problem.
3. Although the control module is powered up, a symptom could exist because of a system fault.
4. Use Tech-1 to aid in diagnosis (to check if serial data is available). If a PROM error is present, the PCM may have been able to flash DTC 12 or 51, but not enable serial data.
5. Although the control module is powered up, a "CRANKS BUT WILL NOT RUN" symptom could exist because of a PCM or system fault.
6. This step will isolate if customer complaint is a MIL or driveability problem with no MIL displayed. See PCM TROUBLE CODE DEFINITIONS table under «TROUBLE CODE DEFINITIONS»(/chevrolet/caprice-impala-ss/1995-1996/remont/automatic-trans/#diagnosis-4l60-e__trouble-code-definitions) , to determine if code is valid. An invalid DTC may be the result of a faulty scan tester, PROM or PCM.
7. Comparison of actual control system data with typical scan tester data values is a quick check to determine if any parameter is not within limits. A base engine problem (i.e. advanced cam timing) may substantially alter sensor values.

On-Board Diagnostic System Flow Chart (Diesel) Courtesy of General Motors Corp. Scheme 137

CHART A-1, NO MIL (SERVICE ENGINE SOON LIGHT)

MIL should be on when engine is off and ignition is on. Switched battery voltage is supplied to MIL. The PCM turns light on by providing a ground path through the MIL (SERVICE ENGINE SOON) control circuit.

Note. Test numbers refer to numbers on diagnostic chart.

1. If fusible link or ECM-B fuse is blown, refer to the «WIRING DIAGRAMS»(/chevrolet/caprice-impala-ss/1995-1996/remont/automatic-trans/#diagnosis-4l60-e) for complete circuit.
2. Using a test light connected to 12 volts, probe each of the system ground circuits to ensure a good ground is present.

If engine functions properly, check for a burned out bulb, blown GAUGES or ALT fuse, or an open in the MIL (SERVICE ENGINE SOON) control circuit. This will result in no brake warning light, oil or generator lights, seat belt reminder, etc.

Chart A-1, Flow Chart (Diesel) Courtesy of General Motors Corp. Scheme 138

CHART A-2, NO SCAN DATA, MIL (SES) ALWAYS ON OR WON'T FLASH

MIL should be on when engine is off and ignition is on. Switched battery voltage is supplied to MIL. The PCM turns light on by providing a ground path through the MIL (SERVICE ENGINE SOON) control circuit. With diagnostic terminal grounded, MIL should flash DTC 12, followed by any other DTC stored in memory. A steady light on indicates a short to ground in the MIL (SERVICE ENGINE SOON) control circuit or an open in the diagnostic request circuit.

Note. Test numbers refer to numbers on diagnostic chart.

1. If there is a problem with PCM that causes scan tester not to read serial data, PCM should not flash DTC 12. If DTC 12 does flash, ensure scan tester is functioning properly (on another vehicle). If scan tester is functioning properly, and serial data circuit is okay, PROM, PCM or SIR DERM may be at fault for the NO DLC symptom.
2. If light goes off when PCM connector is disconnected, MIL (SERVICE ENGINE SOON) control circuit is not shorted to ground.
3. This step checks for an open in the diagnostic request circuit.
4. At this point, MIL wiring is okay. Problem is a faulty PROM. If DTC 12 does not flash, PCM should be replaced using original PROM. Replace PROM only after trying a PCM. A defective PROM usually is an unlikely cause of problem.

Chart A-2, Flow Chart (Diesel) Courtesy of General Motors Corp. Scheme 139

Chart A-3, Circuit Diagram (C & K Series Diesel) Courtesy of General Motors Corp. Scheme 140

Chart A-3, Circuit Diagram (G Series Diesel) Courtesy of General Motors Corp. Scheme 141

This chart assumes battery condition and engine cranking speed are okay, there is adequate fuel in tank, and glow plug system is operating okay.

Note. Test numbers refer to numbers on diagnostic chart.

1. A MIL on is a basic test to determine if there is a 12 volts supply and ignition 12 volts to PCM. No DLC may be due to a PCM problem and CHART A-2 will diagnose PCM.
2. This step will check to see if there is an inject command coming from PCM.
3. This step will check ground circuit.

If no problem is found in fuel pump circuit or ignition system and cause of a "ENGINE CRANKS BUT WILL NOT RUN" has not been found, check for: water or foreign material in fuel system, and/or a basic engine problem.

Note. If crankshaft position sensor and optical sensor are disconnected or inoperable at the same time this will cause an "ENGINE CRANKS BUT WILL NOT RUN" condition.

Chart A-3, Flow Chart (Diesel) Courtesy of General Motors Corp. Scheme 142

DTC 14, Circuit Diagram (C & K Series Diesel) Courtesy of General Motors Corp. Scheme 143

DTC 14, Circuit Diagram (G Series Diesel) Courtesy of General Motors Corp. Scheme 144

Engine Coolant Temperature (ECT) sensor is a thermistor that controls signal voltage to PCM. When engine is cold, sensor resistance is high, and PCM will sense a high signal voltage. As engine warms, sensor resistance becomes less and voltage drops. DTC 14 will set when engine coolant temperature is greater than 304°F (151°C) for 2 seconds.

PCM will default to a engine coolant temperature of 171°F 77°C).

Note. Test numbers refer to numbers on diagnostic chart.

1. This step determines if DTC 14 is the result of a hard failure or an intermittent condition.
2. This step determines if ECT signal circuit is shorted to ground.

Check wiring harness routing for a potential short circuit to ground. After starting engine, coolant temperature should rise to about 185°F (85°C). PCM default value will flash on data screen intermittently.

Test engine coolant temperature sensor at various temperature levels to evaluate possibility of a skewed (mis-scaled) sensor. See TEMPERATURE VS. RESISTANCE VALUES table. A skewed sensor could result in poor driveability complaints.

DTC 14, Flow Chart (Diesel) Courtesy of General Motors Corp. Scheme 145

DTC 15, ECT SENSOR CKT HIGH (LOW TEMPERATURE INDICATED)

Engine Coolant Temperature (ECT) sensor is a thermistor that controls signal voltage to PCM. When engine is cold, sensor resistance is high, and PCM will sense a high signal voltage. As engine warms, sensor resistance becomes less and voltage drops. DTC 15 will set when engine coolant temperature is less than -33°F (-36°C) and engine has been running for at least 8 minutes.

PCM will default to a engine coolant temperature of 64°F 18°C) and increase idle speed.

Note. Test numbers refer to numbers on diagnostic chart.

1. This step determines if DTC 15 is the result of a hard failure or an intermittent condition.
2. This step determines if ECT signal circuit is open or for a faulty PCM.

Check wiring harness routing for a potential short circuit to ground. After starting engine, coolant temperature should rise to about 185°F (85°C). PCM default value will flash on data screen intermittently.

Test engine coolant temperature sensor at various temperature levels to evaluate possibility of a skewed (mis-scaled) sensor. See TEMPERATURE VS. RESISTANCE VALUES table. A skewed sensor could result in poor driveability complaints.

DTC 15, Flow Chart (Diesel) Courtesy of General Motors Corp. Scheme 146

DTC 24, Circuit Diagram (C & K Series Diesel) Courtesy of General Motors Corp. Scheme 147

DTC 24, Circuit Diagram (G Series Diesel) Courtesy of General Motors Corp. Scheme 148

Vehicle Speed Sensor (VSS) circuit consists of a magnetic induction type sensor, VSS buffer module, 4WD low switch (if equipped), and wiring. Gear teeth pressed onto output shaft induces an alternating voltage into sensor. This signal is transmitted to VSS buffer module. VSS buffer module compensates for various final drive ratios. VSS buffer module will also convert AC VSS signal into a 40 pulse per revolution DC signal on trans output speed circuit to indicate transmission output speed. On 4WD vehicles, 4WD low signal will also be used for adjustment of 40 pulse per revolution signal to PCM.

DTC 24 will set when

1. Gear selector is not in Park or Neutral.
2. Trans output speed circuit voltage is constant.
3. Engine speed is greater than 3000 RPM.
4. Output speed is less than 250 RPM.
5. MAP is less than 100 kPa.
6. Throttle position is 10-100 percent.
7. All conditions are met for 3 seconds.
8. DTCs 21, 22, 28, 33 or 34 are not set. PCM will default to 2nd gear only at maximum line pressure. NOTE: Test numbers refer to test numbers on diagnostic chart.

1. This test checks for voltage to VSS buffer module.
2. This test checks ground circuit to VSS buffer module.
3. This test checks VSS circuit at VSS buffer module.
4. This test checks for an output speed signal from VSS buffer module.

DTC 24 will set when no vehicle speed is detected at vehicle start off. DTC 72 will set when vehicle speed has been detected and is lost.

DTC 28, Circuit Diagram (Diesel) Courtesy of General Motors Corp. Scheme 149

Transmission range pressure switch assembly consists of 5 pressure switches (2 normally closed, 3 normally open), and a fluid temperature sensor combined into one unit and mounted on valve body. PCM supplies voltage to each range signal. By grounding one or more of these circuits through various combinations of pressure switches, PCM detects which manual valve position has been selected. With ignition on and engine off, Park/Neutral will be indicated. When transmission electrical connector is disconnected, ground potential for the 3 signals to PCM will be removed, and with ignition on, D2 will be indicated. DTC 28 will set when range signals "A" and "C" are both zero volts (on) for 2 seconds.

PCM will default to harsh shifts, D4 shift control. TCC will be inhibited, and if in hot mode, 4th gear will not be available. DTC 28 will be stored in PCM memory, but will not turn on MIL.

Note. Test numbers refer to numbers on diagnostic chart.

1. This test checks indicated range signal to manual valve position actually selected.
2. This test checks for correct voltage from PCM to transmission external connector.
3. This test checks for short to ground from PCM to transmission external connector in any one of the 3 circuits.

DTC 28 will set if PCM detects one of 2 illegal combinations. See TRANSMISSION RANGE PRESSURE SWITCH COMBINATIONS table. Check all wiring connectors for proper terminal tension. For current DTC 28, range signal will default to D4 while A/B/C range values continue to read actual trans. range pressure switch output for each range selection.

TRANSMISSION RANGE PRESSURE SWITCH COMBINATIONS (1)

DTC 37/38, Circuit Diagram (Diesel) Courtesy of General Motors Corp. Scheme 150

Normally closed brake switch supplies a B+ signal on TCC brake switch signal circuit to PCM. When brakes are applied signal voltage is opened.

DTC 37 will set when

1. TCC brake switch signal circuit is open.
2. Vehicle speed is less than 5 MPH for greater than 6 seconds.
3. Then vehicle speed is 5-20 MPH for greater than 6 seconds.
4. Then vehicle speed is greater than 20 MPH for greater than 6 seconds.
5. For a total of 7 times.

DTC 38 will set when

1. TCC brake switch signal circuit has constant voltage.
2. Vehicle speed is greater than 20 MPH for greater than 6 seconds.
3. Then vehicle speed is 5-20 MPH for greater than 6 seconds.
4. For a total of 7 times.

PCM will default to an incorrect brake signal can affect TCC scheduling. Also, an incorrect brake signal can inhibit 4th gear operation, if in hot mode. DTCS 37/38 will be stored in PCM memory, but will not turn on MIL.

Note. Test numbers refer to numbers on diagnostic chart.

1. This test checks for voltage at brake switch.
2. This test checks brake switch.
3. This test checks TCC brake switch signal circuit at PCM.

If DTC is intermittent, check customer driving habits and/or for unusual traffic conditions (stop and go, expressway traffic).

DTC 52/53, Circuit Diagram (Diesel) Courtesy of General Motors Corp. Scheme 151

Battery voltage input circuit is battery feed for PCM. Ignition voltage input circuit is ignition feed for PCM. DTC 52 will set when ignition is on and PCM battery voltage input circuit terminal voltage is greater than 16 volts for 109 minutes.

DTC 53 will set when ignition is on and PCM battery voltage input circuit terminal voltage is greater than 19.5 volts for 2 seconds.

PCM will default to the pressure control solenoid is turned off, 3-2 control solenoid is turned off, transmission shifts immediately to 3rd gear, and TCC operation will be inhibited. The setting of additional DTCs may result.

Note. Test numbers refer to numbers on diagnostic chart.

1. This test checks that normal battery voltage is 9-15 volts.
2. This test checks if generator is faulty under load conditions.

Battery voltage input circuit supplies battery voltage to PCM. Charging battery with a battery charger and jump-starting an engine may set DTCs 52/53. If DTC sets when an accessory is operated, check for faulty connections or excessive current draw. Check for faulty connections at starter solenoid or fusible link.

DTC 58, TRANS. FLUID TEMP. SENSOR CK LOW HIGH TEMPERATURE INDICATED)

Transmission Fluid Temperature (TFT) sensor is a thermistor within transmission range pressure switch assembly, that controls signal voltage to PCM. PCM applies voltage on 5V TFT signal circuit to sensor. When transmission fluid is cold, sensor resistance is high and PCM will sense high signal voltage.

As transmission fluid temperature warms to normal transmission operating temperature of 212°F (100°C), sensor resistance becomes less and voltage decreases to 1.5-2.0 volts. If DTC 79 is also set, check transmission cooling system. DTC 58 will set when signal voltage indicates TFT greater than 306°F (151°C) for one second.

PCM will default to when DTC 58 is set, transmission will use a warm value for operation, but scan tester will display actual fluid temperature. TCC solenoid will be on in 3rd and 4th gears. Shifts will occur early. DTC 58 will be stored in PCM memory but will not turn on MIL.

Note. Test numbers refer to numbers on diagnostic chart.

1. This test checks for a short to ground or a skewed sensor.
2. This test checks for an internal fault within transmission by creating an open.

Check harness routing for a potential short to ground in 5V TFT signal circuit. Scan tester TFT display should rise steadily to about 212°F (100°C) then stabilize.

Test transmission fluid temperature sensor at various temperature levels to evaluate the possibility of a skewed (mis-scaled) sensor. See TEMPERATURE VS. RESISTANCE VALUES table. A skewed sensor could result in delayed garage shifts or TCC complaints.

TEMPERATURE VS. RESISTANCE VALUES

DTC 59, TRANS. FLUID TEMP. SENSOR CKT HIGH LOW TEMPERATURE INDICATED)

Transmission Fluid Temperature (TFT) sensor is a thermistor within transmission range pressure switch assembly that controls signal voltage to the PCM. PCM applies voltage on 5-volt TFT signal circuit to sensor. When transmission fluid is cold, sensor resistance is high and PCM will sense high signal voltage.

As transmission fluid temperature warms to normal transmission operating temperature of 212°F (100°C), sensor resistance becomes less and voltage decreases to 1.5-2.0 volts. DTC 59 will set when signal voltage indicates TFT less than 40°F (40°C) for one second.

PCM will default to when DTC 59 is set, transmission will use a warm value for operation, but scan tester will display actual fluid temperature. TCC may not apply properly. DTC 59 will be stored in PCM memory but will not turn on MIL.

Note. Test numbers refer to numbers on diagnostic chart.

1. This test checks for a skewed sensor.
2. This test simulates a DTC 58. If PCM recognizes low signal voltage (high temperature), and scan tester displays 295°F (146°C) or greater, PCM and wiring are okay.
3. This test checks if 5-volt TFT signal circuit is open. Five volts should be present at sensor connector when measure using DVOM.

Scan tester displays transmission fluid temperature in degrees. After transmission is operating, temperature should rise steadily to about 212°F (100°C) then stabilize. A faulty connection or open in sensor ground circuit or 5-volt TFT signal circuit may cause DTC 59 to set.

Test transmission fluid temperature sensor at various temperature levels to evaluate possibility of a skewed (mis-scaled) sensor. See TEMPERATURE VS. RESISTANCE VALUES table. A skewed sensor could result in firm shifts or TCC complaints.

TEMPERATURE VS. RESISTANCE VALUES

DTC 66, Circuit Diagram (C & K Series Diesel) Courtesy of General Motors Corp. Scheme 152

DTC 66, Circuit Diagram (G Series Diesel) Courtesy of General Motors Corp. Scheme 153

Hydraulically, the 3-2 control solenoid coordinates apply rate of 2-4 band with hydraulic release, of 3-4 clutch during a 3-2 downshift. PCM continually monitors 3-2 circuit duty cycle depending on commanded state of circuit. When transmission is in 1st gear, duty cycle of solenoid is equal to zero. When transmission is in 2nd gear or higher, duty cycle of solenoid will be about 90 percent. When transmission downshifts, 3-2, duty cycle of solenoid will drop. DTC 66 will set when

1. PCM commands solenoid on and voltage remains high (B+) for 4 seconds.
2. PCM commands solenoid off and voltage remains low (zero volts) for 4 seconds.

PCM will default to a delayed (soft) landing to 3rd gear and 3rd gear starts.

Note. Test numbers refer to numbers on diagnostic chart.

1. This test checks function of 3-2 control solenoid and internal transmission harness.
2. This test checks for power to 3-2 control solenoid from ignition through fuse.

Check all connections at transmission connector. 3-2 control solenoid feedback normally oscillate on/off when duty cycle is applied. An open in ignition feed circuit will cause multiple DTCS to set.

DTC 67, Circuit Diagram (C & K Series Diesel) Courtesy of General Motors Corp. Scheme 154

DTC 67, Circuit Diagram (G Series Diesel) Courtesy of General Motors Corp. Scheme 155

Ignition voltage is supplied directly to TCC solenoid. PCM controls solenoid by providing ground path through TCC control circuit. DTC 67 will set when

1. PCM commands solenoid on and voltage remains high (B+) for 2 seconds.
2. PCM commands solenoid off and voltage remains low (zero volts) for 2 seconds.

PCM will default to no TCC and no 4th gear in hot mode.

Note. Test numbers refer to numbers on diagnostic chart.

1. This test checks PCM's ability to control solenoid.
2. This test checks power supply to TCC solenoid.

Check all connections at transmission connector. Some slight TCC slip is normal. An open in ignition feed circuit will cause multiple DTCS to set. A short to ground in TCC circuit may also cause DTC 69 to set. If TCC circuit is shorted to ground, TCC will hydraulically engage in D2.

DTC 69, Circuit Diagram (C & K Series Diesel) Courtesy of General Motors Corp. Scheme 156

DTC 69, Circuit Diagram (G Series Diesel) Courtesy of General Motors Corp. Scheme 157

PCM energizes TCC solenoid by grounding TCC control circuit with an internal quad-driver. When grounded (energized) by PCM, TCC solenoid stops converter signal oil from exhausting. TCC solenoid will de-energize when quad-driver no longer provides a ground. When TCC solenoid is de-energized, it will block exhaust fluid and release TCC.

DTC 69 will set when

1. DTCs 21, 22 or 28 are not set.
2. TCC slip speed indicates -20 to 20 RPM.
3. TCC solenoid is commanded off.
4. TP sensor signal is greater than 25 percent.
5. Trans. range switch indicates D3 or D4.
6. Commanded gear indicates 3rd or 4th gear.
7. Engine speed is greater than 300 RPM.
8. All conditions are met for 4 seconds. PCM will default to early shift pattern. NOTE: Test numbers refer to numbers on diagnostic chart.

1. This test checks mechanical state of TCC. When PCM commands TCC solenoid off, TCC slip speed should increase.

If TCC is mechanically stuck on, vehicle speed is zero, brakes are applied and D2 is selected, TCC fluid will mechanically apply TCC causing an engine stall.

DTC 72, VEHICLE SPEED SENSOR CIRCUIT LOSS (TRANS OUTPUT SPEED SIGNAL)

Vehicle Speed Sensor (VSS) circuit consists of a magnetic induction type sensor, VSS buffer module, 4WD low switch (if equipped) and wiring. Gear teeth pressed onto output shaft induces an alternating voltage into sensor. This signal is transmitted to VSS buffer module. VSS buffer module compensates for various final drive ratios. VSS buffer module will also convert AC VSS signal into a 40 pulse per revolution DC signal on trans. output speed circuit to indicate transmission output speed. On 4WD vehicles, 4WD low signal will also be used for adjustment of the 40 pulse per revolution signal to PCM.

DTC 72 will set when gear selector is not in Park or Neutral and

1. Trans. output speed change is greater than 1000 RPM.
2. Engine speed is greater than 200 RPM.
3. All conditions are met for 2 seconds.
4. DTC 28 is not set.

Or when gear selector is in Park or Neutral and

1. Trans. output speed change is greater than 2050 RPM.
2. Engine speed is greater than 200 RPM.
3. All conditions are met for 2 seconds.
4. DTC 28 is not set.

PCM will default to a soft (delayed) downshift to 2nd gear and 2nd gear starts.

Note. Test numbers refer to test numbers on diagnostic chart.

1. This test checks for voltage to VSS buffer module.
2. This test checks ground circuit to VSS buffer module.
3. This test checks VSS circuit at VSS buffer module.
4. This test checks for an output speed signal from VSS buffer module.

DTC 24 will set when no vehicle speed is detected at vehicle start off. DTC 72 will set when vehicle speed has been detected and is lost.

DTC 73, Circuit Diagram (Diesel) Courtesy of General Motors Corp. Scheme 158

Pressure control solenoid is a PCM-controlled device used to regulate transmission line pressure. PCM compares TP voltage, engine RPM and other inputs to determine line pressure appropriate for a given load. PCM will regulate pressure by applying a varying amperage to pressure control solenoid. The applied amperage can vary from .1-1.1 amp. PCM then monitors amperage at the return line.

DTC 73 will set when return amperage varies greater than .16 amp from commanded amperage for at least one second and DTC 75 is not set.

PCM will default to full line pressure being applied, causing harsh shifts. DTC 73 will be stored in PCM memory but will not turn on MIL.

Note. Test numbers refer to test numbers on diagnostic chart.

1. This test checks PCM's ability to command pressure control solenoid.
2. This test checks internal transmission harness and pressure control solenoid for correct resistance.

Check for poor connections at PCM and transmission connector.

DTC 75, SYSTEM VOLTAGE LOW

Battery voltage input circuit is battery feed for PCM. Ignition voltage input circuit is ignition feed for PCM. DTC 75 will set when ignition is on and PCM battery voltage input terminal voltage is less than graduated scale of

1. 40°F (-40°C) equals 7.3 volts
2. 194°F (90°C) equals 10.3 volts
3. 304°F (150°C) equals 11.7 volts with engine speed greater than 1000 RPM for 4 seconds.

Pressure control solenoid is turned off, soft landing to default 3rd gear and TCC operation is inhibited. The setting of additional DTCs may result. DTC 75 will be stored in PCM memory but will not turn on MIL.

Note. Test numbers refer to numbers on diagnostic chart.

1. This test checks that normal battery voltage is 9-15 volts.
2. This test checks if low voltage display is due to generator, battery voltage input circuit or PCM, while engine is running. If voltage is less than 8.6 volts, PCM is okay.

Battery voltage input circuit supplies battery voltage to PCM. Charging battery with a battery charger and jump-starting an engine may set DTC 53. If DTC sets when an accessory is operated, check for faulty connections or excessive current draw. Check for faulty connections at starter solenoid or fusible link.

DTC 79, TRANSMISSION FLUID OVERTEMP

Transmission Fluid Temperature (TFT) sensor is a thermistor within transmission range pressure switch assembly, that controls signal voltage to PCM. PCM applies voltage on 5-volt TFT signal circuit to sensor. When transmission fluid is cold, sensor resistance is high and PCM will sense high signal voltage.

As transmission fluid temperature warms to normal transmission operating temperature of 212°F (100°C), sensor resistance becomes less and voltage decreases to 1.5-2.0 volts. DTC 79 will set when signal voltage indicates TFT greater than 295°F (146°C) for 30 seconds, and DTC 58 or 59 is not set.

DTC 79 will be stored in PCM memory but will not turn on MIL.

Note. Test numbers refer to numbers on diagnostic chart.

1. This test checks for a shorted circuit or a skewed sensor.
2. This test simulates a DTC 59.

Check harness routing for a potential short to ground in 5-volt TFT signal circuit. Scan tester TFT display should rise steadily to about 212°F (100°C) then stabilize.

Test transmission fluid temperature sensor at various temperature levels to evaluate possibility of a skewed (mis-scaled) sensor. See TEMPERATURE VS. RESISTANCE VALUES table. A skewed sensor could result in delayed garage shifts or TCC complaints.

TEMPERATURE VS. RESISTANCE VALUES

DTC 81, Circuit Diagram (C & K Series Diesel) Courtesy of General Motors Corp. Scheme 159

DTC 81, Circuit Diagram (G Series Diesel) Courtesy of General Motors Corp. Scheme 160

Ignition voltage is supplied directly to 2-3 shift solenoid. PCM controls solenoid by providing ground path through 2-3 shift solenoid control circuit. DTC 81 will set when PCM commands solenoid on and voltage remains high for 2 seconds, or PCM commands solenoid off and voltage remains low for 2 seconds.

If solenoid is shorted off, 3rd gear only will occur. If solenoid is shorted on, 2nd gear only will occur. DTC 81 will be stored in PCM memory but will not turn on MIL.

Note. Test numbers refer to numbers on diagnostic chart.

1. This test checks the function of 2-3 shift solenoid and internal transmission wiring.
2. This test checks for power to 2-3 shift solenoid from ignition, through fuse.

Check all connections at transmission. An open in ignition feed circuit can cause multiple DTCs to set.

DTC 82, Circuit Diagram (C & K Series Diesel) Courtesy of General Motors Corp. Scheme 161

DTC 82, Circuit Diagram (G Series Diesel) Courtesy of General Motors Corp. Scheme 162

Ignition voltage is supplied directly to 1-2 shift solenoid. PCM controls solenoid by providing ground path through 1-2 shift solenoid control circuit. DTC 82 will set when PCM commands solenoid on and voltage remains high for 2 seconds, or PCM commands solenoid off and voltage remains low for 2 seconds.

PCM will only allow 2nd and 3rd gear, or 1st and 4th gear. DTC 82 will be stored in PCM memory but will not turn on MIL.

Note. Test numbers refer to numbers on diagnostic chart.

1. This test checks the function of 1-2 shift solenoid and internal transmission wiring.
2. This test checks for power to 1-2 shift solenoid from ignition through fuse.

Check all connections at transmission. An open in ignition feed circuit can cause multiple DTCs to set.

DTC 83, Circuit Diagram (C & K Series Diesel) Courtesy of General Motors Corp. Scheme 163

DTC 83, Circuit Diagram (G Series Diesel) Courtesy of General Motors Corp. Scheme 164

TCC PWM is used in combination with TCC solenoid to regulate fluid to torque converter and attached to transmission control valve body. PCM supplies a ground, allowing current to flow through solenoid coil according to duty cycle (percentage of on and off time). This current flow through solenoid coil creates a magnetic field that magnetizes the solenoid core. The magnetized core attracts the check ball to seat against spring pressure. This blocks the exhaust for the TCC signal fluid and allows 2-3 drive fluid to feed TCC signal circuit. TCC signal fluid pressure acts on TCC regulator valve to regulate line pressure and to apply fluid pressure to torque converter clutch shift valve. When TCC shift valve is in apply position, regulated fluid pressure is directed through TCC valve to apply torque converter clutch.

DTC 83 will set when

1. PCM commands solenoid on and voltage remains high (B+).

Or

1. PCM commands solenoid off and voltage remains low (zero volt).
2. All conditions are met for 2 seconds.

PCM will default to inhibit TCC operation and inhibit 4th gear operation if in hot mode.

Note. Test numbers refer to numbers on diagnostic chart.

1. This test checks if PCM is commanding TCC solenoid on.
2. This test checks for voltage to solenoid.

Check all connections, especially those at transmission pass-thru connector.

Following charts are DTC specific. For terminal locations, see WIRING DIAGRAMS . For engine-related DTCs, see appropriate TESTS W/CODES article in ENGINE PERFORMANCE section.

Diagnostic aids located in many trouble code charts are additional tips used to help diagnose trouble codes when circuit checks do not find a problem.

Note. In following diagnostic tests, schematics and illustrations are courtesy of General Motors Corp. Powertrain Control Module (PCM) may also be referred to as Electronic Control Module (ECM) or Transmission Control Module (TCM) in some diagnostic charts and figures. Terms are used interchangeably.

Coolant sensor uses a thermistor to control signal voltage to Vehicle Control Module (VCM). VCM applies and monitors a 5 volts to sensor. When engine coolant is cold, sensor (thermistor) resistance is high and VCM will sense a high signal voltage. As engine coolant warms, sensor resistance becomes less and VCM voltage drops. With Code P0117 set, VCM will turn cooling fans on and use a default engine coolant temperature value based on run time. VCM will illuminate Malfunction Indicator Light (MIL).

Note. Test numbers refer to numbers on diagnostic chart.

1. This step determines if conditions necessary to set Code P0117 exist.
2. Simulates Code P0118. If VCM recognizes high signal voltage, VCM and wiring are okay.
3. Determines if 5-volt reference is open. This determines if there is a wiring problem or faulty VCM.

Code P0117, Circuit Diagram (4.3L S & T Series) Courtesy of General Motors Corp. Scheme 165

Code P0117, Flow Chart (4.3L S & T Series) Courtesy of General Motors Corp. Scheme 166

Tech 1 displays engine temperature in degrees Celsius (°C) and Fahrenheit (°F). After engine is started, temperature should rise steadily to 194°F (90°C), then stabilize when thermostat opens. An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside insulation. Check for

Poor Connection Or Damaged Harness

Inspect VCM harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection, and damaged harness.

Intermittent Test

Using Tech 1, monitor engine coolant temperature while moving related connectors and wiring harness. If failure is induced, display will change. This may assist in isolating location of malfunction.

Shifted Sensor

See TEMPERATURE-TO-RESISTANCE VALUES - "S" & "T" 4 .3L (VIN W) table to test ECT sensor at various temperature levels to evaluate the possibility of a out-of-range sensor which may result in driveability complaints.

Note. A faulty connection, or an open in sensor circuits will cause Code P0117 to set.

TEMPERATURE-TO-RESISTANCE VALUES - "S" & "T" 4.3L (VIN W)

Coolant sensor uses a thermistor to control signal voltage to VCM. VCM applies and monitors a 5 volts to sensor. When engine coolant is cold, sensor (thermistor) resistance is high and VCM will sense a high signal voltage. As engine coolant warms, sensor resistance becomes less and VCM voltage drops. With Code P0118 set, VCM will turn cooling fans on and use a default engine coolant temperature value based on run time. VCM will illuminate Malfunction Indicator Light (MIL).

Note. Test numbers refer to numbers on diagnostic chart.

1. This step determines if conditions necessary to set code exist.
2. Simulates Code P0117. If VCM recognizes low voltage, VCM and wiring are okay.

Code P0118, Flow Chart (4.3L S & T Series) Courtesy of General Motors Corp. Scheme 167

Code P0118, Circuit Diagram (4.3L S & T Series) Courtesy of General Motors Corp. Scheme 168

Tech 1 displays engine temperature in degrees Celsius (°C) and Fahrenheit (°F). After engine is started, temperature should rise steadily to 194°F (90°C), then stabilize when thermostat opens. An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside insulation. Check the following for

1. A short to ground in 5-volt reference circuit.

Using Tech 1, monitor engine coolant temperature while moving related connectors and wiring harness. If failure is induced, display will change. This may assist in isolating location of malfunction.

See TEMPERATURE-TO-RESISTANCE VALUES - "S" & "T" 4 .3L (VIN W) table to test ECT sensor at various temperature levels to evaluate the possibility of a out-of-range sensor which may result in driveability complaints.

TEMPERATURE-TO-RESISTANCE VALUES - "S" & "T" 4.3L (VIN W)

Throttle Position (TP) sensor provides a voltage signal that changes relative to throttle blade angle. Signal voltage will vary from .20-.74 volt at idle to greater than 4 volts at Wide Open Throttle (WOT). TP sensor signal is one of the most important inputs used by VCM for fuel control and for most other VCM control outputs.

Note. Test numbers refer to numbers on diagnostic chart.

1. Determines if conditions necessary to set code exist.
2. Simulates Code P0123 (high voltage). If VCM recognizes high signal voltage, VCM and wiring are okay.
3. Simulates a high signal voltage. Checks signal circuit for an open.

Code P0122, Circuit Diagram (4.3L S & T Series) Courtesy of General Motors Corp. Scheme 169

Tech 1 displays throttle position in volts. Voltage should increase steadily as throttle is moved toward WOT.

An open or short to ground in reference and signal circuits will cause code to set. Check for

Inspect VCM harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection, and damaged harness.

Monitor TP sensor voltage display on Tech 1 while moving related connectors and wiring harness. If failure is induced, display will change. This may assist in isolating location of malfunction.

TP Sensor Scaling

Observe TP sensor voltage display while depressing accelerator pedal with engine stopped and ignition on. Display should vary from closed throttle TP sensor voltage when throttle is closed (less than 1.25 volts) to greater than 4.5 volts when throttle is held at WOT position.

Throttle Position (TP) sensor provides a voltage signal that changes relative to throttle blade angle. Signal voltage will vary from about .5 volt or at idle to about 4 volts at Wide Open Throttle (WOT). TP sensor signal is one of the most important inputs used by VCM for fuel control and for most other VCM control outputs. On non-adjustable TPS sensors, each time voltage drops below 1.25 volts and stops, VCM assumes this value as 0 throttle angle and measures percent throttle from this point on.

With Code P0123 set, throttle position will default to 19 percent and Tech 1 will not indicate fault value. VCM will illuminate Malfunction Indicator Light (MIL).

Note. Test numbers refer to numbers on diagnostic chart.

1. If TP signal is greater than 4.8 volts, fault is present.
2. With TP sensor disconnected, TP sensor voltage should decrease. This test verifies that VCM and wiring are okay.
3. Probing ground circuit with a test light checks sensor ground circuit. This isolates a faulty sensor, VCM or open ground circuit.

Code P0123, Flow Chart (4.3L S & T Series) Courtesy of General Motors Corp. Scheme 170

Tech 1 displays throttle position in volts. With closed throttle, ignition on, or at idle, voltage should be .45-.85 volt. If voltage is not as specified, replace TP sensor. Check for

Inspect VCM harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection, and damaged harness.

Monitor TP sensor voltage display on Tech 1 while moving related connectors and wiring harness. If failure is induced, display will change. This may assist in isolating location of malfunction.

Observe TP sensor voltage display while depressing accelerator pedal with engine stopped and ignition on. Display should vary from closed throttle TP sensor voltage when throttle is closed (less than 1.25 volts) to greater than 4.5 volts when throttle is held at WOT position.

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks VSS circuit.
2. Checks integrity of sensor.
3. Checks 5-volt and ground circuits to VCM.

Code P0502/503, Circuit Diagram (4.3L S & T Series) Courtesy of General Motors Corp. Scheme 171

Code P0502/503, Flow Chart (4.3L S & T Series) Courtesy of General Motors Corp. Scheme 172

Code P0502 will set if no vehicle speed is detected at start off. Code P0503 will set when vehicle speed has been detected and lost. Inspect all harnesses and related wiring, including VCM connectors.

Note. Test numbers refer to numbers on diagnostic chart.

1. Verifies normal charging system voltage is between 13.0 and 15.8 volts.
2. Checks actual battery voltage against voltage at VCM.

Code P0560, Circuit Diagram (4.3L S & T Series) Courtesy of General Motors Corp. Scheme 173

Code P0560, Flow Chart (4.3L S & T Series) Courtesy of General Motors Corp. Scheme 174

Charging battery with a battery charger and jump-starting engine may set this code. If code sets when an accessory is operated, check for faulty connections or excessive current draw. Check for faulty connections at starter solenoid and fusible link. Check for loose or damaged terminals at generator. Check belt tension and wear.

TCC brake switch input is used by VCM to determine when to energize TCC solenoid.

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks for voltage at brake switch.
2. Checks brake switch.
3. Checks TCC brake switch signal at VCM.

Code P0703, Circuit Diagram (4.3L S & T Series) Courtesy of General Motors Corp. Scheme 175

Code P0703, Flow Chart (4.3L S & T Series) Courtesy of General Motors Corp. Scheme 176

Check customer driving habits and/or unusual traffic conditions, i.e. stop and go freeway traffic. Check brake switch adjustment. Check for most current VCM calibration software.

VCM sends a voltage signal to sensor and monitors return voltage. Transmission temperature sensor varies resistance as temperature of transmission fluid changes. Temperature sensor resistance is high when transmission fluid is cold. As fluid temperature increases, sensor resistance decreases.

Note. Test numbers refer to test numbers on diagnostic chart.

1. Checks for short to ground or sensor out-of-range.
2. Checks for an internal fault within transmission by creating an open.

Code P0712, Circuit Diagram (4.3L S & T Series) Courtesy of General Motors Corp. Scheme 177

Code P0712, Flow Chart (4.3L S & T Series) Courtesy of General Motors Corp. Scheme 178

After engine is started, temperature should rise steadily to about 212°F (100°C). Check sensor for shifted calibration by using sensor TEMPERATURE-TO-RESISTANCE VALUES table. An intermittent may be caused by a poor connection, chaffed wire insulation or a broken wire. Monitor voltage of each terminal while moving related harness connectors. If failure is induced, voltage reading will change.

TEMPERATURE-TO-RESISTANCE VALUES

VCM sends a voltage signal to sensor and monitors return voltage. Transmission temperature sensor varies resistance as temperature of transmission fluid changes. Temperature sensor resistance is high when transmission fluid is cold. As fluid temperature increases, sensor resistance decreases.

Note. Test numbers refer to test numbers on diagnostic chart.

1. Verifies a problem in sensor circuit.
2. Simulates Code P0712. If VCM recognizes low signal voltage, VCM and wiring are okay.
3. Checks 5-volt reference for open. There should be 5 volts present at sensor connector.

Code P0713, Flow Chart (4.3L S & T Series) Courtesy of General Motors Corp. Scheme 179

After engine is started, temperature should rise steadily to about 212°F (100°C). Check sensor for shifted calibration by using sensor TEMPERATURE-TO-RESISTANCE VALUES table. An intermittent may be caused by a poor connection, chaffed wire insulation or a broken wire. Monitor voltage of each terminal while moving related harness connectors. If failure is induced, voltage reading will change.

TEMPERATURE-TO-RESISTANCE VALUES

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks mechanical state of TCC when VCM commands TCC solenoid off. TCC slip speed should increase.

Code P0742, Circuit Diagram (4.3L S & T Series) Courtesy of General Motors Corp. Scheme 180

Code P0742, Flow Chart (4.3L S & T Series) Courtesy of General Motors Corp. Scheme 181

Check for proper TP sensor operation. If TCC is mechanically stuck on, vehicle speed is zero, brakes are applied, and D2 is selected, TCC fluid will mechanically apply TCC, causing an engine stall.

Pressure control solenoid is used to regulate transmission line pressure. VCM compares TPS voltage, engine RPM and other inputs to determine proper line pressure for a given load. VCM regulates pressure by applying a varying amperage to pressure control solenoid. Amperage varies from 0.1 to 1.1 amps.

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks ability of VCM to command pressure control solenoid.
2. Checks for voltage at VCM.

Code P0748, Flow Chart (4.3L S & T Series) Courtesy of General Motors Corp. Scheme 182

Check for poor connections at VCM and at transmission connector.

Voltage is supplied directly to solenoid. VCM energizes solenoid by providing a ground circuit for solenoid.

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks 1-2 shift solenoid and internal transmission for shorts.
2. Checks for power to 1-2 shift solenoid from ignition through fuse.

Code P0753, Circuit Diagram (4.3L S & T Series) Courtesy of General Motors Corp. Scheme 183

Code P0753, Flow Chart (4.3L S & T Series) Courtesy of General Motors Corp. Scheme 184

Check all connections at transmission. An open in ignition feed circuit can cause multiple codes to set.

Circuiot Description

Voltage is supplied directly to solenoid. VCM energizes solenoid by providing a ground circuit for solenoid.

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks function of transmission range switch.
2. Checks for proper selected gear ratio.

Code P0756, Circuit Diagram (4.3L S & T Series) Courtesy of General Motors Corp. Scheme 185

Code P0756, Flow Chart (4.3L S & T Series) Courtesy of General Motors Corp. Scheme 186

Check all related wiring, including VCM connectors. A 4WD switch/wiring problem may set this code.

Voltage is supplied directly to solenoid. VCM energizes solenoid by providing a ground circuit for solenoid.

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks 2-3 shift solenoid and internal transmission for shorts.
2. Checks for power to 2-3 shift solenoid from ignition through fuse.
3. Checks ability of VCM and wiring to control ground (driver) circuit.

Code P0758, Flow Chart (4.3L S & T Series) Courtesy of General Motors Corp. Scheme 187

Check all related wiring, including VCM connectors. An open ignition feed circuit may set this code.

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks indicated range to actual manual valve position.
2. Checks for correct voltage from VCM to transmission external connector.
3. Checks for a short to ground or an open in any one of the 3 circuits.

Code P1810, Flow Chart (4.3L S & T Series) Courtesy of General Motors Corp. Scheme 188

Check scan tester accompanying value combinations chart. Check all wiring connectors for proper connections and tension.

VALUE COMBINATION CHART

Transmission fluid temperature sensor is a thermistor which controls signal voltage to VCM. VCM applies and monitors voltage to sensor. When transmission fluid is cold, sensor resistance is high; therefore, VCM will see high signal voltage. As transmission fluid warms, sensor resistance and voltage will drop. At normal transmission operating temperature of 212°F (100°C), voltage will be about 1.5-2.0 volts.

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks for out-of-range sensor or shorted circuit.
2. Simulates Code P0713.

Code P1812, Flow Chart (4.3L S & T Series) Courtesy of General Motors Corp. Scheme 189

Check harness routing for a potential short to ground in signal circuit. Scan tester displays transmission fluid temperature in degrees Centigrade. After transmission is running, temperature display should rise steadily to about 212°F (100°C) then stabilize. Test transmission sensor at various temperature levels to determine if sensor is out of calibration. See TEMPERATURE-TO-RESISTANCE VALUES table. An out-of-calibration sensor could result in delayed shifts or TCC enabled complaint.

TEMPERATURE-TO-RESISTANCE VALUES

Note. Test numbers refer to numbers on diagnostic chart.

1. This test checks if VCM is commanding solenoid on.
2. This test checks for voltage to solenoid.

Code P1860, Circuit Diagram (4.3L S & T Series) Courtesy of General Motors Corp. Scheme 190

Code P1860, Flow Chart (4.3L S & T Series) Courtesy of General Motors Corp. Scheme 191

Check all connections, especially those at transmission pass-thru connector.

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks VCM's ability to control solenoid.
2. Checks power supply to TCC solenoid.

Code P1864, Circuit Diagram (4.3L S & T Series) Courtesy of General Motors Corp. Scheme 192

Code P1864, Flow Chart (4.3L S & T Series) Courtesy of General Motors Corp. Scheme 193

Some slight TCC slip is normal. An open in ignition feed circuit will cause multiple codes to set. A short to ground in TCC circuit may also cause Code P0742 to set.

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks indicated range signal to actual selected range. A faulty switch could set this code.
2. Checks TCC for slippage while in a commanded lock-up state.

Code P1870, Flow Chart (4.3L S & T Series) Courtesy of General Motors Corp. Scheme 194

An intermittent incorrect engine speed signal lasting more than 10 seconds could set this code. A 1-2 (A) shift solenoid stuck off or a 2-3 (B) shift solenoid stuck on could set this code.

Note. Test numbers refer to numbers on diagnostic chart.

1. Checks function of 3-2 control solenoid and internal transmission harness.
2. Checks power to 3-2 solenoid from ignition through fuse.

Code P1886, Circuit Diagram (4.3L S & T Series) Courtesy of General Motors Corp. Scheme 195

Code P1886, Flow Chart (4.3L S & T Series) Courtesy of General Motors Corp. Scheme 196

Check all connections at transmission connector. An open ignition feed circuit will cause multiple codes to set.

COMPONENT & WIRING HARNESS RESISTANCE CHECK

1. Install Jumper Harness (J-39775) to transmission 20-pin connector. Using an ohmmeter, measure resistance between specified terminals for each component. (Scheme 197) Compare resistance reading to known values. See «TRANSMISSION COMPONENT RESISTANCE SPECIFICATIONS»(/chevrolet/caprice-impala-ss/1995-1996/remont/automatic-trans/#diagnosis-4l60-e) table.
2. If resistance reading is okay, go to next step. If resistance reading is not okay, disconnect wiring harness at component and measure component resistance. Replace component if resistance is not as specified. If resistance is as specified, repair wiring harness between component and 20-pin connector.
3. Measure resistance between ground and each terminal at transmission 20-pin connector. (Scheme 197) Resistance should be more than 250 k/ohms for each solenoid and less than 10 megohms for transmission temperature and vehicle speed sensors. Resistance for temperature sensor will vary with temperature. If resistance is within specification, problem is intermittent. If resistance is low, disconnect wiring harness at component.
4. Measure resistance between component terminals and ground. If resistance is low, replace component. If resistance is high, inspect wiring harness for short to ground. Repair as necessary.

PRESSURE SWITCH ASSEMBLY

Install Jumper Harness (J39775) to transmission 20-pin connector. Compare resistance of pressure switches with gear selector in each position to known values. (Scheme 198) If resistance values are the same as chart, problem is intermittent. If resistance values are not the same, complete chart until problem is found.

TRANSMISSION COMPONENT RESISTANCE SPECIFICATIONS

Identifying Component & Connector Terminal Locations Courtesy of General Motors Corp. Scheme 197

Pressure Switch Assembly Resistance Chart Courtesy of General Motors Corp. Scheme 198

TECHNICAL SERVICE BULLETINS (TSB)

Note. Review TSBs before using diagnostic charts to ensure problems are not addressed by these TSBs.

1995 "C", "G" & "K" Series Trucks & Vans With 5.7L (VIN K) & 4L60-E (GM TSB No. 67-65-16 2/96)

PCM may set false Codes 13, 32, 44 or 45 (O2S or EGR diagnostics). Cause of false code(s) is due to system diagnostics not optimally calibrated for non-O2S and non-EGR equipped vehicles. To correct this condition, replace PROM with NEW calibration programmed into it. See PROM IDENTIFICATION table.

PROM IDENTIFICATION

If replacement of PCM is required, see PCM APPLICATION table to identify correct PCM for specified year.

PCM APPLICATION

1995 "L" & "M" Series W/ 4.3L RPO 35, VIN Prior To 255435 On Chevrolet & 559796 On GMC (GM TSB No. 57-71-1910/95)

A driveline growl and/or vibration in 4th gear may occur after TCC is applied. This condition occurs when TCC apply speed is too low. To correct this condition, replace PROM with appropriate updated part. See PROM IDENTIFICATION table. Prior to replacement, check vehicle PROM identification to ensure vehicle was not already updated.

PROM IDENTIFICATION

This 2 part technical bulletin is designed to cover in depth diagnostic strategies for Vehicle Speed Sensor. Bulletin is model specific and includes circuit and component testing and conditions which may cause DTC 72 to set (loose connections, poor ground connections, add-on components which may cause electromagnetic interference). This bulletin may be used in addition to diagnostic procedures for DTC 72 in this article.

1993-95 "C", "G", "K" & "T" 4WD Vehicles (ATRA TSB No. 343)

Vehicles may have one or all of the following conditions

1. Lack of power, especially when carrying loads or during heavy acceleration.
2. Early upshifts regardless of throttle position.
3. Late shifts in 4WD-Low position only.
4. Erratic shifting including shifts which are early during one upshift sequence and normal during next sequence, or some of the upshifts during shift sequence are early while others are normal.
5. Incorrect forced downshift shift points or no forced downshifts at normal road speeds.

These conditions may occur on either 2WD or 4WD vehicles, but are most common on 4WD vehicles. These conditions may be intermittent and could occur without setting trouble codes. If any of these conditions occur, perform following test to assist in diagnosis.

Early, Late Or Erratic Shifts (All Models)

1. Check for trouble codes which may relate to condition. If no codes are present, go to next step. If codes are present, correct affected systems, then check for correct shift timing. If condition still exists, go to next step.
2. Operate vehicle through 2/4 high position shifts. If shifts are early and/or erratic, go to next step. If shifts are late and/or erratic, go to step 5). If shifts are correct, problem is intermittent. Operate vehicle until condition occurs, then repeat step 1). If condition does not occur, check for stuck 4WD switch, loose connections at PCM and 4WD switch, or for circuits which may be shorted to ground. Repair as necessary.
3. Using a scan tool, monitor 4WD-low input. If 4WD-low input indicates low position even though vehicle is in high position, go to next step. If 4WD-low input indicates truck is not in low position, scan tool value for 4WD-low reading will be NO at all times. If condition exists, check TP sensor, MAP sensor or VSS sensor for proper operation. Repair or replace as necessary.
4. Scan tool value for 4WD-low position will be YES at all times if 4WD-low input indicates low position even though vehicle is in high position. A short to ground in 4WD-low position circuit, 4WD switch or related circuit may exist. Perform appropriate 4WD-LOW DIAGNOSTIC CHECK.
5. Check TP sensor, MAP sensor or VSS sensor for proper operation. Repair or replace as necessary. If sensors are okay, check tire size and axle ratio. If tire size and axle ratio has been modified from stock applications, buffer (DRAC) must be recalibrated or replaced with correct calibration.

4WD-Low Diagnostic Check ("K" Series With Manually Or Electronically Shifted Transfer Case In High Position)

1. Disconnect transfer case switch connector at transfer case. Turn ignition switch to ON position. Using a scan tool, monitor 4WD-low position. If scan tool indicates YES for 4WD-low position, go to next step. If scan tool indicates NO for 4WD-low position, check for internal short to ground in transfer case switch. Replace switch as necessary.
2. A short to ground in Dark Blue wire (Gray/Black wire on vehicles with VCM) between transfer case switch connector and PCM terminal F8 (terminal No. 23 on vehicles with VCM), or a faulty PCM/VCM is indicated.
3. Disconnect connector located behind distributor at center of torque converter housing. If scan tool indicates YES for 4WD-low position, go to next step. If scan tool indicates NO for 4WD-low position, check for short to ground in Dark Blue wire (Gray/Black wire on vehicles with VCM) between transfer case switch and connector located behind distributor. Repair wire as necessary.
4. Turn ignition off. Disconnect PCM Blue connector (Black connector on vehicles with VCM). Using an ohmmeter, measure resistance between ground and PCM Blue connector terminal F8 (terminal No. 23 on vehicles with VCM). If resistance is less than 100 ohms, repair short to ground in Dark Blue wire (Gray/Black wire on vehicles with VCM).

4WD-Low Diagnostic Check ("T" Series With PCM & Manually Shifted Transfer Case In High Position)

1. Disconnect 6-pin power distribution center connector located at left kick panel. Turn ignition switch to ON position. Using a scan tool, monitor 4WD-low position. If scan tool indicates YES for 4WD-low position, go to step 4).
2. If scan tool indicates NO for 4WD-low position, check for short to ground in Gray/Black wire between 6-pin connector and shift quadrant switch, or check for a faulty shift quadrant switch, located to right of shift lever at console. Repair as necessary. If wire and switch are okay, connect 6-pin connector and disconnect indicator assembly connector, located forward of shift lever.
3. If scan tool still indicates NO, check for short to ground in indicator assembly or shift quadrant switch. Repair as necessary. If scan tool indicates YES, check for short to ground in Gray/Black wire between 6-pin connector and indicator assembly connector. Repair as necessary.
4. A short to ground in Gray/Black wire between 6-pin connector and PCM terminal F8, or a faulty PCM is indicated. Turn ignition off. Disconnect PCM Blue connector. Using an ohmmeter, backprobe from PCM Blue connector terminal F8 to ground. If resistance is less than 100 ohms, repair short to ground in Gray/Black wire.

4WD-Low Diagnostic Check ("T" Series With VCM & Manually Shifted Transfer Case In High Position)

1. Disconnect in-line connector (Gray/Black wire) located behind glove box. Turn ignition switch to ON position. Using a scan tool, monitor 4WD-low position. If scan tool indicates YES for 4WD-low position, go to step 4).
2. If scan tool indicates NO for 4WD-low position, check for short to ground in Gray/Black wire between in-line connector and shift quadrant switch, or check for a faulty shift quadrant switch, located to right of shift lever at console. Repair as necessary. If wire and circuit and switch are okay, connect in-line connector and disconnect indicator assembly connector, located forward of shift lever.
3. If scan tool still indicates NO, check for short to ground in indicator assembly or shift quadrant switch. Repair as necessary. If scan tool indicates YES, check for short to ground in Gray/Black wire between in-line connector and indicator assembly connector. Repair as necessary.
4. A short to ground in Gray/Black wire between in-line connector and VCM terminal No. 23, or a faulty VCM is indicated. Turn ignition off. Disconnect VCM Black connector. Using an ohmmeter, backprobe from VCM Black connector terminal No. 23 to ground. If resistance is less than 100 ohms, repair short to ground in Gray/Black wire.

4WD-Low Diagnostic Check ("T" Series With Electronically Shifted Transfer Case In High Position)

1. Disconnect 16-pin connector from Transfer Case Control Module (TCCM). On 1993-1994 1/2 vehicles with PCM, TCCM is mounted to PCM. Connector is located behind glove box. On 1994 1/2-1995 vehicles with PCM, connector is located in center of dash, behind ash tray. On vehicles with VCM, connector is located in center of dash, behind ash tray.
2. On all models, turn ignition switch to ON position. Using a scan tool, monitor 4WD-low position. If scan tool indicates YES for 4WD-low position, go to step 4).
3. If scan tool indicates NO for 4WD-low position, check for internal short to ground in TCCM or a stuck selector switch exists. On vehicles with PCM, Dark Green/White wire is shorted to battery voltage. Repair as necessary.
4. A short to ground in Gray/Black wire between 16-pin connector and PCM terminal F8 (terminal No. 23 on vehicles with VCM), or a faulty PCM/VCM is indicated. Turn ignition off. Disconnect PCM Blue connector (Black connector on vehicles with VCM) and TCCM 16-pin connector. Using an ohmmeter, measure resistance between ground and PCM Blue connector terminal F8 (terminal No. 23 on vehicles with VCM). If resistance is less than 100 ohms, repair short to ground in Gray/Black wire.

1995 "B" Body - 4.3L & 5.7L (Caprice, Impala SS & Roadmas Wiring Diagramter). Scheme 199

1995 "D" Body - 5.7L (Fleetwood) Wiring Diagram. Scheme 200

1995 "F" Body - 3.4L (Camaro & Firebird) Wiring Diagram. Scheme 201

1995 "F" Body - 3.8L (Camaro & Firebird) Wiring Diagram. Scheme 202

1995 "F" Body - 5.7L (Camaro & Firebird) Wiring Diagram. Scheme 203

1995 "Y" Body - 5.7L (Corvette) Wiring Diagram. Scheme 204

1995 "C" & "K" Series - 4.3L, 5.0L & 5.7L (Pickup, Sierra, Suburban, Tahoe & Yukon) Wiring Diagram. Scheme 205

1995 "C" & "K" Series - 6.5L (Pickup) Wiring Diagram. Scheme 206

1995 "G" Series - 4.3L, 5.0L & 5.7L (Van) Wiring Diagram. Scheme 207

1995 "L" & "M" Series - 4.3L (Astro & Safari) Wiring Diagram. Scheme 208

1995 "S" & "T" Series - 2.2L & 4.3L VIN Z (Blazer, Jimmy, Pickup & Sonoma) Wiring Diagram. Scheme 209

1995 "S" & "T" Series - 4.3L VIN W With PCM (Blazer, Jimmy, Pickup & Sonoma) Wiring Diagram. Scheme 210

1995 "S" & "T" Series - 4.3L VIN W With VCM (Blazer, Jimmy, Pickup & Sonoma) Wiring Diagram. Scheme 211

See also:
• CLUTCH & BAND APPLICATION
• APPLICATION
• COMPONENT TESTS
• CLEARING TROUBLE CODES
• TROUBLE CODE DEFINITIONS